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#### Class 12th Physics - Semiconductor Electronics Materials Devices And Simple Circuits Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

When the diode is forward biased, it is found that beyond forward voltage V = Vk, called knee voltage, the conductivity is very high. At this value of battery biasing for p-n junction,the potential barrier is overcome and the current increases rapidly with increase in forward voltage. When the diode is reverse biased, the reverse bias voltage produces a very small current about a few microamperes which almost remains constant with bias. This small current is reverse saturation current.
(i) In which of the following figures, the p-n diode is forward biased.

(ii) Based on the V-I characteristics of the diode, we can classify diode as

 (a) bi-directional device (b) ohmic device (c) non-ohmic device (d) passive element

(iii) The V-I characteristic of a diode is shown in the figure. The ratio of forward to reverse bias resistance is

 (a) 100 (b) 106 (c) 10 (d) 10-6

(iv) In the case of forward biasing of a p-n junction diode, which one of the following figures correctly depicts the direction of conventional current (indicated by an arrow mark)?

(v) If an ideal junction diode is connected as shown, then the value of the current I is

 (a) 0.013 A (b) 0.02 A (c) 0.01 A (d) 0.1 A

• 2)

Rectifier is a device which is used for converting alternating current or voltage into direct current or voltage. Its working is based on the fact that the resistance of p-n junction becomes low when forward biased and becomes high when reverse biased. A half-wave rectifier uses only a single diode while a full wave rectifier uses two diodes as shown in figures (a) and (b) .

(i) If the rms value of sinusoidal input to a full wave rectifier is $\frac{V_{0}}{\sqrt{2}}$ then the rms value of the rectifier's output is

 $\text { (a) } \frac{V_{0}}{\sqrt{2}}$ $\text { (b) } \frac{V_{0}^{2}}{\sqrt{2}}$ $\text { (c) } \frac{V_{0}^{2}}{2}$ $\text { (d) } \sqrt{2} V_{0}^{2}$

(ii) In the-diagram, the input ac is actoss the terminals A and C. The output across Band D is

 (a) same as the input (b) half wave rectified (c) zero (d) full wave rectified

(iii) A bridge rectifier is shown in figure. Alternating input is given across A and C. If output is taken across BD, then it is

 (a) zero (b) same as input (c) half wave rectified (d) full wave rectified

(iv) A p-n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit. The current (I) in the resistor(R) can be shown by

(v) With an ac input from 50 Hz power line, the ripple frequency is

 (a) 50 Hz in the dc output of half wave as well as full wave rectifier (b) 100 Hz in the de output of half wave as well as full wave rectifier (c) 50 Hz in the de output of half wave and 100 Hz in dc output offull wave rectifier (d) 100 Hz in the dc output of half wave and 50 Hz in the de output of full wave rectifier

• 3)

From Bohr's atomic model, we know that the electrons have well defined energy levels in an isolated atom. But due to interatomic interactions in a crystal, the electrons of the outer shells are forced to have energies different from those in isolated atoms. Each energy level splits into a number of energy levels forming a continuous band.The gap between top of valence band and bottom of the conduction band in which no allowed energy levels for electrons can exist is called energy gap.

(i) In an insulator energy band gap is

 (a) Eg= 0 (b) Eg< 3eV (c) Eg> 3eV (d) None of the above

(ii) In a semiconductor, separation between conduction and valence band is of the order of

 (a) 0 eV (b) 1 eV (c) 10 eV (d) 50 eV

(iii) Based on the band theory of conductors, insulators and semiconductors, the forbidden gap is smallest in

 (a) conductors (b) insulators (c) semiconductors (d) All of these

(iv) Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

 (a) The number of free electrons for conduction is significant only in Si and Ge but small in C. (b) The number of free conduction electrons is significant in C but small in Si and Ge. (c) The number of free conduction electrons is negligibly small in all the three. (d) The number offree electrons for conduction is significant in all the three.

(v) Solids having highest energy level partially filled with electrons are

 (a) semiconductor (b) conductor (c) insulator (d) none of these

• 4)

Light emitting diode is a photoelectric device which converts electrical energy into light energy. It is a heavily doped p-n junction diode which under forward biased emits spontaneous radiation. The general shape of the J- V characteristics of an LED is similar to that of a normal p-n junction diode, as shown. The barrier potentials are much higher and slightly different for each colour.

(i) The J- V characteristic of an LED is

(ii) The schematic symbol of light emitting diode is (LED)

(iii) An LED is constructed from a p-n junction based on a certain Ga-As-P semiconducting material whose energy gap is 1.9 eV. Identify the colour of the emitted light.

 (a) Blue (b) Red (c) Violet (d) Green

(iv) Which one of the following statement is not correct in the case of light emitting diodes?

 (a) It is a heavily doped p-n junction. (b) It emits light only when it is forward biased. (c) It emits light only when it is reverse biased. (d) The energy of the light emitted is less than the energy gap of the semiconductor used

(v) The energy of radiation emitted by LED is

 (a) greater than the band gap of the semiconductor used (b) always less than the band gap of the semiconductor used (c) always equal to the band gap of the semiconductor used (d) equal to or less than the band gap of the semiconductor used.

• 5)

A photodiode is an optoelectronic device in which current carriers are generated by photons through photoexcitation i.e., photo conduction by light. It is a p-n junction fabricated from a photosensitive semiconductor and provided with a transparent window so as allow light to fall on its function. A photodiode can turn its current ON and OFF in nanoseconds. So, it can be used as a fastest photo-detector.

(i) A p-n photo diode is fabricated from a semiconductor with a band gap of 2.5 ev' It can detect a signal of wavelength

 (a) 4000 nm (b) 6000 nm (c) 4000 $\dot A$ (d) 6000 $\dot A$

(ii) Three photo diodes D1 D2 and D3 are made of semiconductors having band gap of 2.5 eV, 2 eV and 3 eV, respectively. Which one will be able to detect light of wavelength 6000 $\dot A$ ?

 (a) D1 (b) D2 (c) D3 (d) D1, and D2 both

(iii) Photodiode is a device

 (a) which is always operated in reverse bias (b) which of always operated in forward bias (c) in which photo current is independent of intensity of incident radiation (d) which may be operated in forward or reverse bias.

(iv) To detect light of wavelength 500 nrn, the photodiode must be fabricated from a semiconductor of minimum bandwidth of

 (a) 1.24 eV (b) 0.62 eV (c) 2.48eV (d) 3.2 eV

(v) Photo diode can be used as a photo detector to detect

 (a) optical signals (b) electrical signals (c) both (a) and (b) (d) none of these

#### Class 12th Physics - Nuclei Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

In the year 1939, German scientist Otto Hahn and Strassmann discovered that when an uranium isotope was bombarded with a neutron, it breaks into two intermediate mass fragments. It was observed that, the sum of the masses of new fragments formed were less than the mass of the original nuclei. This difference in the mass appeared as the energy released in the process. Thus, the phenomenon of splitting of a heavy nucleus (usually A> 230) into two or more lighter nuclei by the bombardment of proton, neutron, a-particle, etc with liberation of energy is called nuclear fission.
${ }_{92} \mathrm{U}^{235}+{ }_{0} n^{1} \rightarrow \quad{ }_{92} \mathrm{U}^{236} \rightarrow{ }_{56} \mathrm{Ba}^{144}+{ }_{36} \mathrm{Kr}^{89}+3{ }_{0} n^{1}+Q$
Unstable nucleus
(i) Nuclear fission can be explained on the basis of

 (a) Millikan's oil drop method (b) Liquid. drop model (c) Shell model (d) Bohr's model

(ii) For sustaining the nuclear fission chain reaction in a sample (of small size) ${ }_{92}^{235} \mathrm{U}$, it is desirable to slow down fast neutrons by

 (a) friction (b) elastic damping/scattering (c) absorption (d) none of these

(iii) Which of the following is/are fission reaction(s)?
$\text { (I) }{ }_{0}^{1} n+{ }_{92}^{235} \mathrm{U} \rightarrow{ }_{92}^{236} \mathrm{U} \rightarrow{ }_{51}^{133} \mathrm{Sb}+{ }_{41}^{99} \mathrm{Nb}+4_{0}^{1} n$
$\text { (II) }{ }_{0}^{1} n+{ }_{92}^{235} \mathrm{U} \rightarrow{ }_{54}^{1.40} \mathrm{Xe}+{ }_{38}^{94} \mathrm{Sr}+2{ }_{0}^{1} n$
$(\mathrm{III}){ }_{1}^{2} \mathrm{H}+{ }_{1}^{2} \mathrm{H} \rightarrow{ }_{2}^{3} \mathrm{He}+{ }_{0}^{1} n$

 (a) Both II and III (b) Both I and III (c) Only II (d) Both I and II

(iv) On an average, the number of neutrons and the energy of a neutron released per fission of a uranium atom are respectively

 (a) 2.5 and 2 keV (b) 3 and 1 keV (c) 2.5 and 2 MeV (d) 2 and 2 keV

(v) In any fission process, ratio of mass of daughter nucleus to mass of parent nucleus is

 (a) less than 1 (b) greater than 1 (c) equal to 1 (d) depends 0 the mass of parent nucleus

• 2)

The nucleus was first discovered in 1911 by Lord Rutherford and his associates by experiments on scattering of a-particles by atoms. He found that the scattering results could be explained, if atoms consist of a small, central, massive and positive core surrounded by orbiting electrons. The experimental results indicated that the size of the nucleus is of the order of 10-14m and is thus 10000 times smaller than the size of atom.
(i) Ratio of mass of nucleus with mass of atom is approximately

 (a) 1 (b) 10 (c) 103 (d) 1010

(ii) Masses of nuclei of hydrogen, deuterium and tritium are in ratio

 (a) 1:2:3 (b) 1:1:1 (c) 1:1:2 (d) 1:2:4

(iii) Nuclides with same neutron number but different atomic number are

 (a) isobars (b) isotopes (c) isotones (d) none of these

(iv) If R is the radius and A is the mass number, then log R versus log A graph will be

 (a) a straight line (b) aparabola (c) anellipse (d) none of these

(v) The ratio of the nuclear radii of the gold isotope ${ }_{79}^{197} \mathrm{Au}$ and silver isotope ${ }_{47}^{107} \mathrm{Au}$ is

 (a) 1.23 (b) 0.216 (c) 2.13 (d) 3.46

• 3)

A heavy nucleus breaks into comparatively lighter nuclei which are more stable compared to the original heavy nucleus. When a heavy nucleus like uranium is bombarded by slow moving neutrons, it splits into two parts releasing large amount of energy. The typical fission reaction of ${ }_{92} \mathrm{U}^{235}$.
${ }_{92} \mathrm{U}^{235}+{ }_{0} n^{1} \rightarrow{ }_{56} \mathrm{Ba}^{141}+{ }_{36} \mathrm{Kr}^{92}+3{ }_{0} n^{1}+200 \mathrm{MeV}$
The fission of 92U235approximately released 200 MeV of energy.
(i) If 200 MeV energy is released in the fission of a single nucleus of ${ }_{92}^{235} \mathrm{U}$,the fissions which are required to produce a power of 1kW is

 (a) 3.125 x 1013 (b) 1.52 x 106 (c) 3.125 x 1012 (d) 3.125 x 1014

(ii) The release in energy in nuclear fission is consistent with the fact that uranium has

 (a) more mass per nucleon than either ofthe two fragments (b) more mass per nucleon as the two fragment (c) exactly the same mass per nucleon as the two fragments (d) less mass per nucleon than either of two fragments.

(iii) When 92U235undergoes fission, about 0.1% of the original mass is converted into energy. The energy released when 1 kg of 92U235undergoes fission is

 (a) 9 x 1011J (b) 9 x 1013J (c) 9 x 1015J (d) 9 x 1018J

(iv) A nuclear fission is said to be critical when multiplication factor or K

 (a) K= 1 (b) K> 1 (c) K< 1 (d) K=0

(v) Einstein's mass-energy conversion relation E = mc2 is illustrated by

 (a) nuclear fission (b) $\beta$-decay (c) rocket propulsion (d) steam engine
• 4)

Neutrons and protons are identical particle in the sense that their masses are nearly the same and the force, called nuclear force, does into distinguish them. Nuclear force is the strongest force. Stability of nucleus is determined
by the neutron proton ratio or mass defect or packing fraction. Shape of nucleus is calculated by quadrupole moment and spin of nucleus depends on even or odd mass number. Volume of nucleus depends on the mass number. Whole mass of the atom (nearly 99%) is centred at the nucleus.
(i) The correct statements about the nuclear force is/are

 (a) change independent (b) short range force (c) non-conservative force (d) all of these.

(ii) The range of nuclear force is the order of

 (a) 2 x 10-10 m (b) 1.5 x 10-20 m (c) 1.2 x 10-4 m (d) 1.4 x 10-15 m

(iii) A force between two protons is same as the force between proton and neutron. The nature of the force is

 (a) electrical force (b) weak nuclear force (c) gravitational force (d) strong nuclear force.

(iv) Two protons are kept at a separation of 40 $\dot A$. Fn is the nuclear force and Fe is the electrostatic force between them. Then

 (a) Fn << Fe (b) Fn = Fe (c) Fn >> Fe (d) Fn $\approx$ Fe

(v) All the nucleons in an atom are held by

 (a) nuclear forces (b) van der Waal's forces (c) tensor forces (d) coulomb forces
• 5)

The density of nuclear matter is the ratio of the mass of a nucleus to its volume. As the volume of a nucleus is directly proportional to its mass number A, so the density of nuclear matter is independent of the size of the nucleus. Thus, the nuclear matter behaves like a liquid of constant density. Different nuclei are like drops of this liquid, of different sizes but of same density.
Let A be the mass number and R be the radius of a nucleus. If m is the average mass of a nucleon, then
Mass of nucleus = mA
$\text { Volume of nucleus }=\frac{4}{3} \pi R^{3}=\frac{4}{3} \pi\left(R_{0} A^{1 / 3}\right)^{3}=\frac{4}{3} \pi R_{0}^{3} A$
$\text { Nuclear density, } \rho_{\mathrm{nu}}=\frac{\text { Mass of nucleus }}{\text { Volume of nucleus }} \text { or } \rho_{\mathrm{nu}}=\frac{m A}{\frac{4}{3} \pi R_{0}^{3} A}=\frac{3 m}{4 \pi R_{0}^{3}}$

Clearly, nuclear density is independent of mass number A or the size of the nucleus. The nuclear mass density is of the order 1017 kg m-3. This density is very large as compared to the density of ordinary matter, say water, for which p = 1.0 x 103 kg m-3.
(i) The nuclear radius of ${ }_{8}^{16} \mathrm{O}$ is 3 X 10-15 m. The density of nuclear matter is

 (a) 2.9 x 1034 kg m-3 (b) 1.2 x 1017kg m-3 (c) 16 x 1027kg m-3 (d) 2.4 x 1017kg m-3

(ii) What is the density of hydrogen nucleus in SI units? Given Ro = 1.1 fermi and mp = 1.007825 amu

 (a) 2.98 x 1017kg m-3 (b) 3.0 x 1034 kg m-3 (c) 1.99 x 1011 kg m-3 (d) 7.85 x 1017kg m-3

(iii) Density of a nucleus is

 (a) more for lighter elements and less for heavier elements. (b) more for heavier elements and less for lighter elements (c) very less compared to ordinary matter (d) a constant

(iv) The nuclear mass of ${ }_{26}^{56} \mathrm{Fe}$ is 55.85 amu. The its nuclear density is

 (a) 5.0 x 1019kg m-3. (b) 1.5 x 1019kg m-3 (c) 2.9 x 1017kg m-3 (d) 9.2 x 1026kg m-3

(v) If the nucleus of ${ }_{13}^{27} \mathrm{Al}$ has a nuclear radius of about 3.6 fm, then ${ }_{52}^{125} \mathrm{Te}$ would have its radius approximately as

 (a) 9.6 fm (b) 12 fm (c) 4.8 fm (d) 6 fm

#### Class 12th Physics - Atoms Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

Niels Bohr introduced the atomic Hydrogen model in 1913. He described it as a positively charged nucleus, comprised of protons and neutrons, surrounded by a negatively charged electron cloud. In the model, electrons orbit the nucleus in atomic shells. The atom is held together by electrostatic forces between the positive nucleus and negative surroundings.

Bohr correctly proposed that the energy and radii of the orbits of electrons in atoms are quantized, with energy for transitions between orbits given by
$\Delta E=h v=E_{i}-E_{f}$ Where $\Delta E$ is the change in energy between the initial and final orbits and hv is the energy of an absorbed or emitted photon.
(i) In the Bohr model of the hydrogen atom, discrete radii and energy states result when an electron circles the atom in an integer number of

 (a) de Broglie wavelengths (b) wave frequencies (c) quantum numbers (d) diffraction patterns.

(ii) The angular speed of the electron in the nth orbit of Bohr's hydrogen atom is

 (a) directly proportional to n (b) inversely proportional to $\sqrt{n}$ (c) inversely proportional to n2 (d) inversely proportional to n3

(iii) When electron jumps from n = 4 level to n = 1 level, the angular momentum of electron changes by

 $\text { (a) } \frac{h}{2 \pi}$ $\text { (b) } \frac{h}{\pi}$ $\text { (c) } \frac{3 h}{2 \pi}$ $\text { (d) } \frac{2 h}{\pi}$

(iv) The lowest Bohr orbit in hydrogen atom has

 (a) the maximum energy (b) the least energy (c) infinite energy (d) zero energy

(v) Which of the following postulates of the Bohr modelled to the quantization of energy of the hydrogen atom?

 (a) The electron goes around the nucleus in circular orbits. (b) The angular momentum of the electron can only be an integral multiple of h/2$\pi$ (c) The magnitude of the linear momentum of the electron is quantized. (d) Quantization of energy is itself a postulate of the Bohr model.
• 2)

In 1911, Rutherford, along with his assistants, H. Geiger and E. Marsden, performed the alpha particle scattering experiment. H. Geiger and E. Marsden took radioactive source $\left(\begin{array}{c} 214 \\ 83 \end{array} \mathrm{Bi}\right)$ for a-particles. A collimated beam of a-particles of energy 5.5 MeV was allowed to fall on 2.1 x 10-7 m thick gold foil. The a-particles were observed through a rotatable detector consisting of a Zinc sulphide screen and microscope. It was found that a-particles got scattered. These scattered a-particles produced scintillations on the zinc sulphide screen. Observations of this experiment are as follows.
(I) Most of the a-particles passed through the foil without deflection.
(II) Only about 0.14% of the incident a-particles scattered by more than 1°.
(III) Only about one a-particle in every 8000 a-particles deflected by more than 90°.
These observations led to many arguments and conclusions which laid down the structure of the nuclear model of an atom.

(i) Rutherford's atomic model can be visualised as

(ii) Gold foil used in Geiger-Marsden experiment is about 10-8 m thick. This ensures

 (a) gold foil's gravitational pull is small or possible (b) gold foil is deflected when a-particle stream is not incident centrally over it (c) gold foil provides no resistance to passage of a-particles (d) most a-particle will not suffer more than 1° scattering during passage through gold foil

(iii) In Geiger-Marsden scattering experiment, the trajectory traced by an a-particle depends on

 (a) number of collision (b) number of scattered a- particles (c) impact parameter (d) none of these

(iv) In the Geiger-Marsden scatteririg experiment, in case of head-on collision, the impact parameter should be

 (a) maximum (b) minimum (c) infinite (d) zero

(v) The fact only a small fraction of the number of incident particles rebound back in Rutherford scattering indicates that

 (a) number of a-particles undergoing head-on-collision is small (b) mass of the atom is concentrated in a small volume (c) mass of the atom is concentrated in a large volume (d) both (a) and (b).
• 3)

At room temperature, most of the H-atoms are in ground state. When an atom receives some energy (i.e., by electron collisions), the atom may acquire sufficient energy to raise electron to higher energy state. In this condition, the atom is said to be in excited state. From the excited state, the electron can fall back to a state of lower energy emitting a photon equal to the energy difference of the orbit.

In a mixture of H-He+ gas (He+ is single ionized He atom), H-atoms and He+ ions are excited to their respective first excited states. Subsequently, H-atoms transfer their total excitation energy to He+ ions (by collisions).
(i) The quantum number n of the state finally populated in He+ ions is

 (a) 2 (b) 3 (c) 4 (d) 5

(ii) The wavelength of light emitted in the visible region by He+ ions after collisions with H-atoms is

 (a) 6.5 x 10-7 m (b) 5.6 x 10-7 m (c) 4.8 x 10-7 m (d) 4.0 x 10-7 m

(iii) The ratio of kinetic energy of the electrons for the H-atoms to that of He+ ion for n = 2 is

 $\text { (a) } \frac{1}{4}$ $\text { (b) } \frac{1}{2}$ (c) 1 (d) 2

(iv) The radius ofthe ground state orbit of H-atoms is

 $\text { (a) } \frac{\varepsilon_{0}}{h \pi m e^{2}}$ $\text { (b) } \frac{h^{2} \varepsilon_{0}}{\pi m e^{2}}$ $\text { (c) } \frac{\pi m e^{2}}{h}$ $\text { (d) } \frac{2 \pi h \varepsilon_{0}}{m e^{2}}$

(v) Angular momentum of an electron in H-atom in first excited state is

 $\text { (a) } \frac{h}{\pi}$ $\text { (b) } \frac{h}{2 \pi}$ $\text { (c) } \frac{2 \pi}{h}$ $\text { (d) } \frac{\pi}{h}$
• 4)

Bohr's model explains the spectral lines of hydrogen atomic emission spectrum. While the electron of the atom remains in the ground state, its energy is unchanged. When the atom absorbs one or more quanta of energy, the electrons moves from the ground state orbit to an excited state orbit that is further away.

The given figure shows an energy level diagram of the hydrogen atom. Several transitions are marked as I, II, III and so on. The diagram is only indicative and not to scale.
(i) In which transition is a Balmer series photon absorbed?

 (a) II (b) III (c) IV (d) VI

(ii) The wavelength of the radiation involved in transition II is

 (a) 291 nm (b) 364 nm (c) 487 nm (d) 652 nm

(iii) Which transition will occur when a hydrogen atom is irradiated with radiation of wavelength 103 nm?

 (a) I (b) II (c) IV (d) V

(iv) The electron in a hydrogen atom makes a transition from n = n1 to n = n2 state. The time period of the electron in the initial state is eight times that in the final state. The possible values of n1 and n2 are

 (a) n1=4,n2=2 (b) n1=8,n2=2 (c) n1=8,n2=3 (d) n1=6,n2=2

(v) The Balmer series for the H-atom can be observed

 (a) if we measure the frequencies of light emitted when an excited atom falls to the ground state (b) if we measure the frequencies of light emitted due to transitions between excited states and the first excited state. (c) in any transition in a H-atom (d) none of these.
• 5)

The spectral series of hydrogen atom were accounted for by Bohr using the relation $\bar{v}=R\left(\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right)$
where R = Rydberg constant = 1.097 x 107 m.
Lyman series is obtained when an electron jumps to first orbit from any subsequent orbit. Similarly, Balmer series is obtained when an electron jumps to 2nd orbit from any subsequent orbit, Paschen series is obtained when an electron jumps to 3rd orbit from any subsequent orbit. Whereas Lyman series lies in U.V. region, Balmer series is in visible region and Paschen series lies in infrared region. Series limit is obtained when n2 =$\infty$
(i) The wavelength of first spectral line of Lyman series is

 (a) 1215.4 $\dot A$ (b) 1215.4 crn (c) 1215.4 m (d) 1215.4 mm

(ii) The wavelength limit of Lyman series is

 (a) 1215.4 $\dot A$ (b) 511.9 $\dot A$ (c) 951.6 $\dot A$ (d) 911.6 $\dot A$

(iii) The frequency of first spectral line of Balmer series is

 (a) 1.097 x 107 Hz (b) 4.57 x 1014 Hz (c) 4.57 x 1015 Hz (d) 4.57 x 1016 Hz

(iv) Which of the following transitions in hydrogen atoms emit photons of highest frequency?

 (a) n=1 to n=2 (b) n=2 to n=6 (c) n=6 to n=2 (d) n=2 to n=1

(v) The ratio of minimum to maximum wavelength in Balmer series is

 (a) 5:9 (b) 5:36 (c) 1:4 (d) 3: 4

#### Class 12th Physics - Dual Nature of Radiation and Matter Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

Photoelectric effect is the phenomenon of emission of electrons from a metal surface, when radiations of suitable frequency fallon them. The emitted electrons are called photoelectrons and the current so produced is called photoelectric current.
(i) With the increase of intensity of incident radiations on photoelectrons emitted by a photo tube, the number of photoelectrons emitted per unit time is

 (a) increases (b) decreases (c) remains same (d) none of these

(ii) It is observed that photoelectron emission stops at a certain time t after the light source is switched on. The stopping potential (V) can be represented as

 (a) 2(KEmax/e) (b) (KEmax/e) (c) (KEmax/3e) (d) (KEmax/2e)

(iii) A point source of light of power 3.2 x 10-3 W emits monoenergetic photons of energy 5.0 eV and work function 3.0 eV. The efficiency of photoelectron emission is 1 for every 106 incident photons. Assume that photoelectrons are instantaneously swept away after emission. The maximum kinetic energy of photon is

 (a) 4 eV (b) 5 eV (c) 2 eV (d) Zero

(iv) Which of the following device is the application of Photoelectric effect?

 (a) Light emitting diode (b) Diode (c) Photocell (d) Transistor

(v) If the frequency of incident light falling on a photosensitive metal is doubled, the kinetic energy of the emitted photoelectron is

 (a) unchanged (b) halved (c) doubled (d) more than twice its initial value
• 2)

When a monochromatic radiations of suitable frequency obtained from source S, after being filtered by a filter attached on the window W, fall on the photosensitive place C, the photo electrons are emitted from C, which get accelerated towards the plate A if it is kept at positive potential. These electrons flow in the outer circuit resulting in photoelectric current. Due to it, the micro ammeter shows a deflection. The reading of micrommeter measures the photoelectric current.

An experimental setup of verification of photoelectric effect is shown in figure. The voltage across the electrodes is measured with the help of an ideal voltmeter, and which can be varied by moving jockey J on the potentiometer wire. The battery used in potentiometer circuit is of 16 V and its internal resistance is 2 $\Omega$  The resistance of 100 ern long po.t•e. ntiometer wire is 8 $\Omega$.

The photocurrent is measured with the help of an ideal ammeter. Two plates of potassium oxide of area 50 cm2 at separation 0.5 mm are used in the vacuum tube. Photocurrent in the circuit is very small, so we can treat the
potentiometer circuit as an independent circuit

 Light Violet blue Green Yellow Orange Red $\lambda$ in $\dot A$ 4000-5000 4500-5000 5000-5500 5500-6000 6000-6500 6500-7000

(i) When radiation falls on the cathode plate, a current of 2 $\mu$A is recorded in the ammeter. Assuming that the vacuum tube setup follows Ohm's law, the equivalent resistance of vacuum tube operating in the case when jockey is at end P is

 (a) 8 x 108$\Omega$ (b) 16 x 106$\Omega$ (c) 8 x 106$\Omega$ (d) 10 x 106$\Omega$

(ii) It is found that ammeter current remains unchanged (2 $\mu$A) even when the jockey is moved from the end P to the middle point of the potentiometer wire. Assuming that all the incident photons eject electrons and the power of the light incident is 4 x 10-6$\Omega$Then, the color of the incident light is

 (a) Green (b) Violet (c) Red (d) Orange

(iii) Which of the following colors may not give photoelectric effect for this cathode?

 (a) Green (b) Violet (c) Red (d) Orange

(iv) When other light falls on the anode plate, the ammeter reading zero till jockey is moved from the end P to the middle point of the wire PQ. Therefore, the deflection is recorded in the ammeter. The maximum kinetic energy of the emitted electron is

 (a) 16 eV (b) 8 eV (c) 4 eV (d) 10 eV

(v) If the intensity of incident radiation is increased twice, the number of photoelectrons emitted per second will be

 (a) halves (b) double (c) remain same (d) four times
• 3)

A point source S of power 6.4 x 10-3W emits mono energetic photons each of energy 6.0 eV.The source is located at a distance of 0·8 m from the centre of a stationary metallic sphere of work function 3·0 eV and of radius 1.6 x 10-3 m as shown in figure. The sphere is isolated and initially neutral and photoelectrons are instantly taken away from sphere after emission. The efficiency of photoelectric emission is one for very 105 incident photons.

 $\text { (a) } \frac{4 R^{2}}{P r}$ $\text { (b) } \frac{P R^{2}}{4 r^{2}}$ $\text { (c) } \frac{p^{2} R}{2 \pi r}$ $\text { (d) } \frac{P R}{4 r}$

(ii) Number of photons striking the metal sphere per second is

 (a) 6.7 x 109 (b) 3.3 x 109 (c) 6.7 x 1010 (b) 3.3 x 1010

(iii) The number of photoelectrons emitted per second is about

 (a) 3.3 x 104 (b) 6.7 x 104 (c) 6.7 x 1015 (d) 3.3 x 1015

(iv) The photoelectric emission stops when the sphere acquires a potential about

 (a) 2 V (b) 3 V (c) 4 V (d) 6 V

(v) If the distance of source becomes double from the centre of the metal sphere then the power received by the sphere

 $\text { (a) } \frac{P R^{2}}{4 r^{2}}$ $\text { (b) } \frac{P R^{2}}{16 r^{2}}$ $\text { (c) } \frac{P R^{2}}{4 r}$ $\text { (d) } \frac{P^{2} R^{2}}{16 r^{2}}$
• 4)

According to Einstein, when a photon of light of frequency u or wavelength $\lambda$ is incident on a photosensitive metal surface of work function $\phi$0w' here $\phi$0< hv (here, h is Planck's constant), then the emission of photoelectrons takes place. The maximum kinetic energy of the emitted photoelectrons is given by Kmax = hv - $\phi$0'If the frequency of the incident light is Vcalled threshold frequency, the photoelectrons are emitted from metal without any kinetic energy. So hv0 = $\phi$
(i) A metal of work function 3·3 eV is illuminated by light of wavelength 300 nm. The maximum kinetic energy of photoelectrons emitted is (taking h = 6·6 x 10-34 Js

 (a) 0.413 eV (b) 0.825 eV (c) 1.65 eV (d) 1.32 eV

(ii) The variation of maximum kinetic energy (Kmax) of the emitted photoelectrons with frequency (v) of the incident radiations can be represented by

(iii) The variation of photoelectric current (i) with the intensity of the incident radiation (I) can be represented by

(iv) The graph between the stopping potential (V0) and $\left(\frac{1}{\lambda}\right)$ is shown in the figure $\phi_{1}, \phi_{2}, \phi_{3}$ 3 are work function. Which of the following options is correct?

 $\text { (a) } \phi_{1}: \phi_{2}: \phi_{3}=1: 2: 3$ $\text { (b) } \phi_{1}: \phi_{2}: \phi_{3}=4: 2: 1$ $\text { (c) } \phi_{1}: \phi_{2}: \phi_{3}=1: 2: 4$ (d) Ultraviolet light can be used to emit photoelectrons from metal 2 and metal 3 only

(v) Which of the following figures represent the variation of particle momentum and the associated de- Broglie wavelength?

• 5)

When light of sufficiently high frequency is incident on a metallic surface, electrons are emitted from the metallic surface. This phenomenon is called photoelectric emission. Kinetic energy of the emitted photoelectrons depends on the wavelength of incident light and is independent of the intensity of light. Number of emitted photoelectrons depends on intensity. (hv - $\phi$ is the maximum kinetic energy of emitted photoelectrons (where $\phi$ is the work function of metallic surface). Reverse effect of photo emission produces X-ray. X-ray is not deflected by electric and magnetic fields. Wavelength of a continuous X-ray depends on potential difference across the tube. Wavelength of characteristic X-ray depends on the atomic number.
(i) Einstein's photoelectric equation is

 $\text { (a) } E_{\max }=h v-\phi$ $\text { (b) } E=m c^{2}$ $\text { (c) } E^{2}=p^{2} c^{2}+m_{0}^{2} c^{4}$ $\text { (d) } E=\frac{1}{2} m v^{2}$

(ii) Light of wavelength $\lambda$ which is less than threshold wavelength is incident on a photosensitive material. If incident wavelength is decreased so that emitted photoelectrons are moving with some velocity then stopping potential will

 (a) increase (b) decrease (c) be zero (d) become exactly half

(iii) When ultraviolet rays incident on metal plate then photoelectric effect does not occur, it occur by incident of

 (a) Infrared rays (b) X-rays (c) Radio wave (d) Micro wave

(iv) Iffrequency (v > v0) of incident light becomes n times the initial frequency (v), then K.E. of the emitted photoelectrons becomes (v0 threshold frequency).

 (a) n times of the initial kinetic energy (b) More than n times of the initial kinetic energy (c) Less than n times of the initial kinetic energy (d) Kinetic energy of the emitted photoelectrons remains unchanged

(v) A monochromatic light is used in a photoelectric experiment. The stopping potential

 (a) Is related to the mean wavelength (b) Is related to the shortest wavelength (c) Is not related to the minimum kinetic energy of emitted photoelectrons (d) Intensity of incident light

#### Class 12th Physics - Wave Optics Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

If double slit apparatus is immersed in a liquid of refractive index, I-l the wavelength of light reduces to $\lambda$ and fringe width also reduces to $\beta^{\prime}=\frac{\beta}{\mu} \text { . }$
The given figure shows a double-slit experiment in which coherent monochromatic light of wavelength A from a distant source is incident upon the two slits, each of width w(w >> $\lambda$) and the interference pattern is viewed on a distant screen. A thin piece of glass of thickness t and refractive index n is placed between one of the slit and the screen, perpendicular to the light path.

(i) In Young's double slit interference pattern, the fringe width

 (a) can be changed only by changing the wavelength of incident light (b) can be changed only by changing the separation between the two slits (c) can be changed either by changing the wavelength or by changing the separation between two sources (d) is a universal constant and hence cannot be changed

(ii) If the width w of one of the slits is increased to 2w, the become the amplitude due to slit

 (a) 1.5a (b) a/2 (c) 2a (d) no change

(iii) In YDSE, let A and B be two slits. Films of thicknesses tA and tB and refractive indices mA and mB are placed in front of A and B, respectively. If $\mu_{\mathrm{A}} t_{A}=\mu_{B} t_{B}$ then the central maxima will

 (a) not shift (b) shift towards A (c) shift towards B (d) shift towards A if tB = tA and shift towards B if tB < tA

(iv) In Young's double slit experiment, a third slit is made in between the double slits. Then

 (a) fringes of unequal width are formed. (b) contrast between bright and dark fringes is reduced (c) intensity of fringes totally disappears (d) only bright light is observed on the screen

(v) In Young's double slit experiment, if one of the slits is covered with a microscope cover slip, then

 (a) fringe pattern disappears (b) the screen just gets illuminated (c) in the fringe pattern, the brightness of the bright fringes will decreases and the dark fringes will become more dark (d) bright fringes will be more bright and dark fringes will become more dark.

• 2)

Distance between two successive bright or dark fringes is called fringe width.
$\beta=Y_{n+1}-Y_{n}=\frac{(n+1) \lambda D}{d}-\frac{n \lambda D}{d}=\frac{\lambda D}{d}$
Fringe width is independent of the order of the maxima. If whole apparatus is immersed in liquid of refractive index $\mu$ then $\beta=\frac{\lambda D}{\mu d}$ (fringe width decreases). Angular fringe width ($\theta$) is the angular separation between two consecutive maxima or minima $\theta=\frac{\beta}{D}=\frac{\lambda}{d}$
In the arrangement shown in figure, slit S3 and S4 are having a variable separation Z. Point 0 on the screen is at the common perpendicular bisector of S1S2 and S3S4.

(i) The maximum number of possible interference maxima for slit separation equal to twice the wavelength in Young's double-slit experiment, is

 (a) infinite (b) five (c) three (d) zero

(ii) In Young's double - slit experiment if yellow light is replaced by blue light, the interference fringes become

 (a) wider (b) brighter (c) narrower (d) darker

(iii) In Young's double slit experiment, if the separation between the slits is halved and the distance between the slits and the screen is doubled, then the fringe width compared to the unchanged one will be

 (a) Unchanged (b) Halved (c) Doubled (d) Quadrupled

(iv) When the complete Young's double slit experiment is immersed in water, the fringes

 (a) remain unaltered (b) become wider (c) become narrower (d) disappear

(v) In a two slit experiment with white light, a white fringe is observed on a screen kept behind the slits. When the screen is moved away by 0.05 m, this white fringe

 (a) does not move at all (b) gets displaced from its earlier position (c) becomes coloured (d) disappears

• 3)

When light from a monochromatic source is incident on a single narrow slit, it gets diffracted and a pattern of alternate bright and dark fringes is obtained on screen, called "Diffraction Pattern" of single slit. In diffraction pattern of single slit, it is found that
(I) Central bright fringe is ·of maximum intensity and the intensity of any secondary bright fringe decreases with increase in its order.
(II) Central bright fringe is twice as wide as any other secondary bright or dark fringe .

(i) A single slit of width 0.1 mm is illuminated by a parallel beam of light of wavelength 6000 A and diffraction bands are observed on a screen 0.5 m from the slit. The distance of the third dark band from the central bright band is

 (a) 3 mm (b) 1.5 mm (c) 9 mm (d) 4.5 mm

(ii) In Fraunhofer diffraction pattern, slit width is 0.2 mm and screen is at 2 m away from the lens. If wavelength of light used is 5000 $\lambda$ then the distance between the first minimum on either side the central maximum is

 (a) 10-1 m (b) 10-2 m (c) 2 x 10-2 m (d) 2 x 10-1 m

(iii) Light of wavelength 600 nm is incident normally on a slit of width 0.2 mm. The angular width of central maxima in the diffraction pattern is (measured from minimum to minimum)

(iv) A diffraction pattern is obtained by using a beam of red light. What will happen, if the red light is replaced by the blue light?

 (a) bands disappear (b) bands become broader and farther apart (c) no change will take place (d) diffraction bands become narrower and crowded together.

(v) To observe diffraction, the size of the obstacle

 (a) should be A/2, where A is the wavelength. (b) should be of the order of wavelength. (c) has no relation to wavelength. (d) should be much larger than the wavelength.

• 4)

In Young's double slit experiment, the width of the central bright fringe is equal to the distance between the first dark fringes on the two sides of the central bright fringe.
In given figure below a screen is placed normal to the line joining the two point coherent source SI and S2' The interference pattern consists of concentric circles.

(i) The optical path difference at P is

 $(a) d\left[1+\frac{y^{2}}{2 D}\right]$ $(b) d\left[1+\frac{2 D}{y^{2}}\right]$ $(c) d\left[1-\frac{y^{2}}{2 D^{2}}\right]$ $(d) d\left[2 D-\frac{1}{y^{2}}\right]$

(ii) Find the radius of the nth bright fringe.

 $(a) D \sqrt{1\left(1-\frac{n \lambda}{d}\right)}$ $(b) D \sqrt{2\left(1-\frac{n \lambda}{d}\right)}$ $(c) 2 D \sqrt{2\left(1-\frac{n \lambda}{d}\right)}$ $(d) D \sqrt{2\left(1-\frac{n \lambda}{2 d}\right)}$

(iii) If d = 0.5 mm, $\lambda$= 5000 $\dot A$and D = 100 em, find the value of n for the closest second bright fringe

 (a) 888 (b) 830 (c) 914 (d) 998

(iv) The coherence of two light sources means that the light waves emitted have

 (a) same frequency (b) same intensity (c) constant phase difference (d) same velocity.

(v) The phenomenon of interference is shown by

 (a) longitudinal mechanical waves only (b) transverse mechanical waves only (c) electromagnetic waves only (d) all of these

• 5)

A narrow tube is bent in the form of a circle of radius R, as shown in figure. Two small holes Sand D are made in the tube at the positions at right angle to each other. A source placed at S generates a wave of intensity Io which is equally divided into two parts: one part travels along the longer path, while the other travels along the shorter path. Both the waves meet at point D where a detector is placed.

(i) If a maxima is formed at a detector, then the magnitude of wavelength $\lambda$ of the wave produced is given by

 $(a) \pi R$ $(b) \frac{\pi R}{2}$ $(c) \frac{\pi R}{4}$ (d) all of these

(ii) If the intensity ratio of two coherent sources used in Young's double slit experiment is 49 : 1, then the ratio between the maximum and minimum intensities in the interference pattern is

 (a) 1: 9 (b) 9: 16 (c) 25: 16 (d) 16: 9

(iii) The maximum intensity produced at D is given by

 (a) 4I0 (b) 2I0 (c) I0 (d) 3I0

(iv) In a Young's double slit experiment, the intensity at a point where the path difference is $\lambda$/6 ($\lambda$ - wavelength of the light) is I. If I0 denotes the maximum intensity, then I/I0 is equal to

 $(a) \frac{1}{2}$ $(b) \frac{\sqrt{3}}{2}$ $(c) \frac{1}{\sqrt{2}}$ $(d) \frac{3}{4}$

(v) Two identical light waves, propagating in the same direction, have a phase difference d. After they superpose the intensity of the resulting wave will be proportional to

 $(a) \cos \delta$ $(b) \cos (\delta / 2)$ $(c) \cos ^{2}(\delta / 2)$ $(d) \cos ^{2} \delta$

#### Class 12th Physics - Ray Optics and Optical Instruments Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

A convex or converging lens is thicker at the centre than at the edges. It converges a parallel beam of light on refraction through it. It has a real focus. Convex lens is of three types:
(i) Double convex lens
(ii) Plano-convex lens
(iii) Concavo-convex lens. Concave lens is thinner at the centre than at the edges. It diverges a parallel beam of light on refraction through it. It has a virtual focus.
(i) A point object 0 is placed at a distance of 0.3 m from a convex lens (focal length 0.2 m) cut into two halves each of which is displaced by 0.0005 m as shown in figure.What will be the location of the image?

 (a) 30 cm right of lens (b) 60 ern right of lens (c) 70 ern left of lens (d) 40 cm left oflens

(ii) Two thin lenses are in contact and the focal length of the combination is 80 cm. If the focal length of one lens is 20 cm, the focal length of the other would be

 (a) -26.7 cm (b) 60 crn (c) 80 cm (d) 20 cm

(iii) A spherical air bubble is embedded in a piece of glass. For a ray of light passing through the bubble, it behaves like a

 (a) converging lens (b) diverging lens (c) plano-converging lens (d) plano-diverging lens

(iv) Lens used in magnifying glass is

 (a) Concave lens (b) Convex lens (c) Both (a) and (b) (d) None of the above

(v) The magnification of an image by a convex lens is positive only when the object is placed

 (a) at its focus F (b) between F and 2F (c) at 2F (d) between F and optical centre
• 2)

Power (P) of a lens is given by-reciprocal of focal length (f) of the lens i.e., $P=\frac{1}{f}$ where fis in metre and P is in dioptre. For a convex lens, power is positive and for a concave lens, power is negative. When a number of thin lenses of powers P1, P2, P3, .....are held in contact with one another, the power of the combination is given by algebraic sum of the powers of all the lenses i.e., P = P1 + P2 + P3 + ....
(i) A convex and a concave lens separated by distance d are then put in contact. The focal length of the combination

 (a) becomes 0 (b) remains the same (c) decreases (d) increases.

(ii) If two lenses of power +1.5D and +1.0D are placed in contact, then the effective power of combination will be

 (a) 2.5 D (b) 1.5D (c) 0.5 D (d) 3.25 D

(iii) If the power of a lens is +5 dioptre, what is the focal length of the lens?

 (a) 10 crn (b) 20 cm (c) 15 crn (d) 5 cm

(iv) Two thin lenses offocallengths +10 cm and -5 em are kept in contact. The power of the combination is

 (a) -10 D (b) -20 D (c) 10 D (d) 15 D

(v) A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm. The system will be

 (a) converging in nature (b) diverging in nature (c) can be converging or diverging (d) None of the above

• 3)

Total internal reflection is the phenomenon of reflection of light into denser medium at the interface of denser medium with a rarer medium. For this phenomenon to occur necessary condition is that light must travel from denser to rarer and angle of incidence in denser medium must be greater than critical angle (C) for the pair of media in contact. Critical angle depends on nature of medium and wavelength of light. We can show that
$\mu=\frac{1}{\sin C} .$
(i) Critical angle for glass air interface, where $\mu$ of glass is $\frac{3}{2}$ is

 (a) 41.8° (b) 60° (c) 30° (d) 15°

(ii) Critical angle for water air interface is 48.6°. What is the refractive index of water?

 (a) 1 (b) $\frac{3}{2}$ (c) $\frac{4}{3}$ (d) $\frac{3}{4}$

(iii) Critical angle for air water interface for violet colour is 49°. Its value for red colour would be

 (a) 49° (b) 50° (c) 48° (d) cannot say

(iv) Which of the following is not due to total internal reflection?

 (a) Working of optical fibre. (b) Difference between apparent and real depth of a pond. (c) Mirage on hot summer days. (d) Brilliance of diamond

(v) Critical angle of glass is $\theta$1 and that of water is $\theta$2, The critical angle for water and glass surface would be $\left(\mu_{g}=3 / 2, \mu_{w}=4 / 3\right)$

 (a) less than $\theta$2 (b) between $\theta$1 and $\theta$2 (c) greater than $\theta$2 (d) less than $\theta$1
• 4)

The lens maker's formula is a relation that connects focal length of a lens to radii of curvature of two surfaces of the lens and refractive index of the material of the lens. It is $\frac{1}{f}=(\mu-1)\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)$ where $\mu$ is refractive index oflens material w.r.t. the medium in which lens is held.As ,$\mu_{v}>\mu_{r}$ therefore $f_{r}>f_{v^{\prime}}$ Mean focal length of lens for yellow colour is $f=\sqrt{f_{r} \times f_{v}}$.
(i) Focal length of a equiconvex lens of glass $\mu=\frac{3}{2}$ in air is 20 cm. The radius of curvature of each surface is

 (a) 10cm (b) -10 crn (c) 20 crn (d) -20 cm

(ii) A substance is behaving as convex lens in air and concave in water, then its refractive index is

 (a) greater than air but less than ater (b) greater than both air and water (c) smaller than air (d) almost equal to water

(iii) For a thin lens with radii of curvatures R1 and R2, refractive index nand focal length f, the factor $\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)$ is equal to

 $(a) \frac{1}{f(n-1)}$ $(b) f(n-1)$ $(c) \frac{(n-1)}{f}$ $(d) \frac{n}{f(n-1)}$

(iv) A given convex lens of glass $\left(\mu=\frac{3}{2}\right)$ can behave as concave when it is held in a medium of $\mu$ equal to

 (a) 1 $\text { (b) } \frac{3}{2}$ $\text { (c) } \frac{2}{3}$ $\text { (d) } \frac{7}{4}$

(v) The radii of curvature of the surfaces of a double convex lens are 20 cm and 40 cm respectively, and its focal length is 20 cm. What is the refractive index of the material of the lens?

 $\text { (a) } \frac{5}{2}$ $\text { (b) } \frac{4}{3}$ $\text { (c) } \frac{5}{3}$ $\text { (d) } \frac{5}{4}$
• 5)

An astronomical telescope is an optical instrument which is used for observing distinct images of heavenly bodies libe stars, planets etc. It consists of two lenses. In normal adjustment of telescope, the final image is formed at infinity. Magnifying power of an astronomical telescope in normal adjustment is defined as the ratio of the angle subtended at the eye by the angle subtended at the eye by the final image to the angle subtended at the eye, by the object directly, when the final image and the object both lie at infinite distance from the eye. It is given by,$m=\frac{f_{0}}{f_{e}}$ To increase magnifying power of an astronomical telescope in normal adjustment, focal length of objective lens should be large and focal length of eye lens should be small.
(i) An astronomical telescope of magnifying power 7 consists of the two thin lenses 40 cm apart, in normal adjustment. The focal lengths of the lenses are

 (a) 5cm,35cm (b) 7cm,35cm (c) 17cm,35cm (d) 5cm,30cm

(ii) An astronomical telescope has a magnifying power of 10. In normal adjustment, distance between the objective and eye piece is 22 cm. The focal length of objective lens is

 (a) 25 cm (b) 10 cm (c) 15 cm (d) 20 cm

(iii) In astronomical telescope compare to eye piece, objective lens has

 (a) negative focal length (b) zero focal length (c) small focal length (d) large focal length

(iv) To see stars, use

 (a) simple microscope (b) compound microscope (c) endoscope (d) astronomical telescope

(v) For large magnifying power of astronomical telescope

 $(a) f_{v}< \((b) f_{v}=f_{\mathrm{e}}$ $(c) f_{o}>>f_{\mathrm{e}}$ (d) none of these

#### Class 12th Physics - Electromagnetic Waves Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

In an electromagnetic wave both the electric and magnetic fields are perpendicular to the direction of propagation, that is why electromagnetic waves are transverse in nature. Electromagnetic waves carry energy as they travel through space and this energy is shared equally by the electric and magnetic fields. Energy density of an electromagnetic waves is the energy in unit volume of the space through which the wave travels.
(i) The electromagnetic waves propagated perpendicular to both $\vec{E} \text { and } \vec{B}$. The electromagnetic waves travel in the direction of

 $(a) \vec{E} \cdot \vec{B}$ $(b) \vec{E} \times \vec{B}$ $(c) \vec{B} \cdot \vec{E}$ $(d) \vec{B} \times \vec{E}$

(ii) Fundame tal particle in an electromagnetic wave is

 (a) photon (b) electron (c) phonon (d) proton

(iii) Electromagnetic waves are transverse in nature is evident by

 (a) polarisation (b) interference (c) reflection (d) diffraction

(iv) For a wave propagating in a medium, identify the property that is independent of the others.

 (a) velocity (b) wavelength (c) frequency (d) all these depend on each other

(v) The electric and magnetic fields of an electromagnetic waves are

 (a) in opposite phase and perpendicular to each other (b) in opposite phase and parallel to each other (c) in phase and perpendicular to each other (d) in phase and parallel to each other.
• 2)

Maxwell showed that the speed of an electromagnetic wave depends on the permeability and permittivity of the medium through which it travels. The speed of an electromagnetic wave in free space is given by $c=\frac{1}{\sqrt{\mu_{0} \varepsilon_{0}}} .$ The fact led Maxwell to predict that light is an electromagnetic wave. The emergence of the speed of light from purely electromagnetic considerations is the crowning achievement of Maxwell's electromagnetic theory. The speed of an electromagnetic wave in any medium of permeability $\mu$ and permittivity $\varepsilon$ will be $\frac{c}{\sqrt{K \mu_{r}}}$ where K is the dielectric constant of the medium and $\mu$r is the relative permeability.
(i) The dimensions of $\frac{1}{2} \varepsilon_{0} E^{2}$ ($\varepsilon$0  permittivity of free space; E = electric field) is

 $(a) \mathrm{MLT}^{-1}$ $(b) \mathrm{ML}^{2} \mathrm{~T}^{-2}$ $(c) \mathrm{ML}^{-1} \mathrm{~T}^{-2}$ $(d) M L^{2} T^{-1}$

(ii) Let [$\varepsilon$0] denote the dimensional formula of the permittivity of the vacuum. If M = mass, L = length, T = time and A = electric current, then

 $(a) \left[\varepsilon_{0}\right]=\mathrm{M}^{-1} \mathrm{~L}^{-3} \mathrm{~T}^{2} \mathrm{~A}$ $(b) \left[\varepsilon_{0}\right]=M^{-1} L^{-3} T^{4} A^{2}$ $(c) \left[\varepsilon_{0}\right]=\mathrm{MLT}^{-2} \mathrm{~A}^{-2}$ $(d) \left[\varepsilon_{0}\right]=\mathrm{ML}^{2} \mathrm{~T}^{-1}$

(iii) An electromagnetic wave of frequency 3MHz passes from vacuum into a dielectric medium with permittivity $\varepsilon$ = 4. Then

 (a) wavelength and frequency both remain unchanged (b) wavelength is doubled and the frequency remains unchanged (c) wavelength is doubled and the frequency becomes half (d) wavelength is halved and the frequency remains unchanged.

(iv) Which of the following are not electromagnetic waves?

 (a) cosmic rays (b) $\Upsilon$-rays (c) $\beta$-rays (d) X-rays

(v) The electromagnetic waves travel with

 (a) the same speed in all media (b) the speed of light c = 3 x 108 m s-1 in free space (c) the speed oflight c = 3 x 108 m S-1 in solid medium (d) the speed of light c = 3 x 108 m s-1 in fluid medium
• 3)

An electromagnetic wave transports linear momentum as it travels through space. If an electromagnetic wave transfers a total energy U to a surface in time t, then total linear momentum delivered to the surface is $p=\frac{U}{c}$ When an electromagnetic wave falls on a surface, it exerts pressure on the surface. In 1903, the American scientists Nichols and Hull succeeded in measuring radiation pressures of visible light where other had failed, by making a detailed empirical analysis of the ubiquitous gas heating and ballistic effects.
(i) The pressure exerted by an electromagnetic wave of intensity I (W m-2) on a non-reflecting surface is (c is the velocity of light)

 (a) Ic (b) Ic2 (c) I/c (d) I/c2

(ii) Light with an energy flux of 18 W/cm2 falls on a non-reflecting surface at normal incidence. The pressure exerted on the surface is

 (a) 2 N/m2 (b) 2 x 10-4 N/m2 (c) 6 N/m2 (d) 6 x 10-4 N/m2

(iii) Radiation of intensity 0.5 W m-2 are striking a metal plate. The pressure on the plate is

 (a) 0.166 x 10-8 N m-2 (b) 0.212 x 10-8 N m-2 (c) 0.132 x 10-8 N m-2 (d) 0.083 x 10-8 N m-2

(iv) A point source of electromagnetic radiation has an average power output of 1500 W The maximum value of electric field at a distance of3 m from this source (in V m-1) is

 (a) 500 (b) 100 $\text { (c) } \frac{500}{3}$ $\text { (c) } \frac{250}{3}$

(v) The radiation pressure of the visible light is of the order of

 (a) 10-2 N m2 (b) 10-4N/m (c) 10-6 N/m2 (d) 10-8N
• 4)

All the known radiations from a big family of electromagnetic waves which stretch over a large range of wavelengths. Electromagnetic wave include radio waves, microwaves, visible light waves, infrared rays, UV rays, X-rays and gamma rays. The orderly distribution of the electromagnetic waves in accordance with their wavelength or frequency into distinct groups having widely differing properties is electromagnetic spectrum.
(i) Which wavelength of the Sun is used finally as electric energy?

 (a) radio waves (b) infrared waves (c) visible light (d) microwaves

(ii) Which of the following electromagnetic radiations have the longest wavelength?

 (a) X-rays (b) $\Upsilon$-rays (c) microwaves (d) radiowaves

(iii) Which one of the following is not electromagnetic in nature?

 (a) X-rays (b) gamma rays (c) cathode rays (d) infrared rays

(iv) Which of the following has minimum wavelength?

 (a) X-rays (b) ultraviolet rays (c) $\Upsilon$-rays (d) cosmic rays

(v) The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is

 (a) microwave, infrared, ultraviolet, gamma rays (b) gamma rays, ultraviolet, infrared, microwave (c) microwave, gamma rays, infrared, ultraviolet (d) infrared, microwave, ultraviolet, gamma rays
• 5)

Electrons oscillating in a circuit give rise to radiowaves. A transmitting antenna radiates most effectively the radiowaves of wavelength equal to the size of the antenna. The infrared waves incident on a substance set into oscillation all its electrons, atoms and molecules. This increases the internal energy and hence the temperature of the substance.
(i) If vg, vx and vm are the speeds of gamma rays, X-rays and microwaves respectively in vacuum, then

 (a) Vg > VX > Vm (b) Vg X m (c) Vg > VX > Vm (d) Vg= VX= Vm

(ii) Which of the following will deflect in electric field?

 (a) X-rays (b) $\Upsilon$-rays (c) cathode rays (d) ultraviolet rays

(iii) $\Upsilon$-rays are detected by

 (a) point contact diodes (b) thermopiles (c) ionization chamber (d) photocells

(iv) The frequency of electromagnetic wave, which best suited to observe a particle of radius 3 x 10-4 cm is the order of

 (a) 1015Hz (b) 1014Hz (c) 1013Hz (d) 1012Hz

(v) We consider the radiation emitted by the human body. Which one of the following statements is true?

 (a) The radiation emitted is in the infrared region. . (b) The radiation is emitted only during the day. (c) The radiation is emitted during the summers and absorbed during the winters (d) The radiation emitted lies in the ultraviolet region and hence it is not visible

#### Class 12th Physics - Alternating Current Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

When a pure resistance R, pure inductor L and an ideal capacitor of capacitance C is connected in series to a source of alternating e.m.f., then current at any instant through the three elements has the same amplitude and is represented as I = Iosinwt. However, voltage across each element has a different phase relationship with the current as shown in graph.
The effective resistance of RLC circuit is called impedance (2) of the circuit and the voltage leads the current by a phase angle $\phi .$

A resistor of $12 \Omega$ a capacitor of reactance $14 \Omega$ and a pure inductor of inductance 0.1 H are joined in series and placed across 200 V, 50 Hz a.c. supply
(i) The value of inductive reactance is

 $\text { (a) } 15 \Omega$ $\text { (b) } 31.4 \Omega$ $\text { (c) } 20 \Omega$ $\text { (d) } 30 \Omega$

(ii) The value of impedance is

 $\text { (a) } 20 \Omega$ $\text { (b) } 15 \Omega$ $\text { (c) } 30 \Omega$ $\text { (d) } 21.13 \Omega$

(iii) What is the value of current in the circuit?

 (a) 5 A (b) 15 A (c) 10 A (d) 9.46 A

(iv) What is the value of the phase angle between current and voltage?

 $\text { (a) } 53^{\circ} 9^{\prime}$ $\text { (b) } 63^{\circ} 9^{\prime}$ $\text { (c) } 55^{\circ} 4^{\prime}$ (d) 50°

(v) From graph, which one is true from following?

 $\text { (a) } V_{L} \geq V_{C}$ $\text { (b) } V_{L}V_{C}$ $\text { (d) } V_{L}=V_{C}$
• 2)

Let a source of alternating e.m.f. E = Eosinrot be connected to a capacitor of capacitance C. If 'I' is the instantaneous value of current in the circuit at instant t, then $I=\frac{E_{0}}{1 / \omega C} \sin \left(\omega t+\frac{\pi}{2}\right)$ The capacitive reactance limits the amplitude of current in a purely capacitive circuit and it is given by $X_{C}=\frac{1}{\omega C}$

(i) What is the unit of capacitive reactance?

 (a) farad (b) ampere (c) ohm (d) ohm -1

(ii) The capacitive reactance of a $5 \mu \mathrm{F}$ lFcapacitor for a frequency of 106 Hz is

 $\text { (a) } 0.032 \Omega$ $\text { (b) } 2.52 \Omega$ $\text { (c) } 1.25 \Omega$ $\text { (d) } 4.51 \Omega$

(iii) In a capacitive circuit, resistance to the flow of current is offered by

 (a) resistor (b) capacitor (c) inductor (d) frequency

(iv) In a capacitive circuit, by what value of phase angle does alternating current leads the e.m.f?

 (a) 45° (b) 90° (c) 75° (d) 60°

(v) One microfarad capacitor is joined to a 200 V, 50 Hz alternator. The rms current through capacitor is

 $\text { (a) } 6.28 \times 10^{-2} \mathrm{~A}$ $\text { (b) } 7.5 \times 10^{-4} \mathrm{~A}$ $\text { (c) } 10.52 \times 10^{-2} \mathrm{~A}$ $\text { (d) } 15.25 \times 10^{-2} \mathrm{~A}$
• 3)

Let a source of alternating e.m.f E = Eosinrot be connected to a circuit containing a pure inductance L. If I is the value of instantaneous current in the circuit, then $I=I_{0} \sin \left(\omega t-\frac{\pi}{2}\right)$.The inductive reactance limits the current in a purely inductive circuit and is given by $X_{L}=\omega L$

(i) A 100 hertz a.c. is flowing in a 14 mH coil. The reactance is

 $\text { (a) } 15 \Omega$ $\text { (b) } 7.5 \Omega$ $\text { (c) } 8.8 \Omega$ $\text { (d) } 10 \Omega$

(ii) In a pure inductive circuit, resistance to the flow of current is offered by

 (a) resistor (b) inductor (c) capacitor (d) resistor and inductor

(iii) In a inductive circuit, by what value of phase angle does alternating current lags behind e.m.f.?

 45o 90o (c) 120° 75o

(iv) How much inductance should be connected to 200 V, 50 Hz a.c. supply so that a maximum current of 0.9 A  flows through it?

 (a) 5 H (b) 1 H (c) 10 H (d) 4.5 H

(v) The maximum value of current when inductance of 2 H is connected to 150 volt, 50 Hz supply is

 (a) 0.337 A (b) 0.721 A (c) 1.521 A (d) 2.522 A
• 4)

The power averaged over one full cycle of a.c. is known as average power. It is also known as true power
$P_{\mathrm{av}}=V_{\mathrm{rms}} I_{\mathrm{rms}} \cos \phi=\frac{V_{0} I_{0}}{2} \cos \phi$
Root mean square or simply rms watts refer to continuous power
A circuit containing a 80.mH inductor and a $60 \mu \mathrm{F}$ capacitor in series is connected to a 230 V, 50 Hz supply. The resistance of the circuit is negligible.

(i) The value of current amplitude is

 (a) 15 A (b) 11.63 A (c) 17.65 A (d) 6.33 A

(ii) Find rms value.

 (a) 6 A (b) 5.25 A (c) 8.23 A (d) 7.52A

(iii) The average power transferred to inductor is

 (a) zero (b) 7W (c) 2.5 W (d) 5 W

(iv) The average power transferred to the capacitor is

 (a) 5 W (b) zero (c) 11 W (d) 15 W

(v) What is the total average power absorbed by the circuit?

 (a) zero (b) 10W (c) 2.5 W (d) 15W
• 5)

A transformer is essentially an a.c. device. It cannot work on d.c. It changes alternating voltages or currents. It does not affect the frequency of a.c. It is based on the phenomenon of mutual induction. A transformer essentially consists of two coils of insulated copper wire having different number of turns and wound on the same soft iron core.
The number of turns in the primary and secondary coils of an ideal transformer are 2000 and 50 respectively. The primary coil is connected to a main supply of 120 V and secondary coil is connected to a bulb of resistance $0.6 \Omega$
(i) The value of voltage across the secondary coil is

 (a) 5V (b) 2V (c) 3 V (d) 10 V

(ii) The value of current in the bulb is

 (a) 7 A (b) 15 A (c) 3 A (d) 5 A

(iii) The value of current in primary coil is

 (a) 0.125 A (b) 2.52 A (c) 1.51 A (d) 3.52 A

(iv) Power in primary coil is

 (a) 20W (b) 5W (c) 10 W (d) 15W

(v) Power in secondary coil is

 (a) 15W (b) 20 W (c) 7W (d) 8 W

#### Class 12th Physics - Electromagnetic Induction Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

Lenz's law states that the direction of induced current in a circuit is such that it opposes the change which produces it. Thus, if the magnetic flux linked with a closed circuit increases, the induced current flows in such a direction that magnetic flux is created in the opposite direction of the original magnetic flux. If the magnetic flux linked with the closed circuit decreases, the induced current flows in such a direction so as to create magnetic flux in the direction of the original flux.

(i) Which of the following statements is correct?

 (a) The induced e.rn.f is not in the direction opposing the change in magnetic flux so as to oppose the cause which produces it. (b) The relative motion between the coil and magnet produces change in magnetic flux. (c) Emf is induced only if the magnet is moved towards coil. (d) Emf is induced only if the coil is moved towards magnet

(ii) The polarity of induced emf is given by

 (a) Ampere's circuital law (b) Biot-Savart law (c) Lenz's law (d) Fleming's right hand rule

(iii) Lenz's law is a consequence of the law of conservation of

 (a) charge (b) mass (c) momentum (d) energy

(iv) Near a circular loop of conducting wire as shown in the figure, an electron moves along a straight line. The direction of the induced current if any in the loop is

 (a) variable (b) clockwise (c) anticlockwise (d) zero

(v) Two identical circular coils A and B are kept in a horizontal tube side by side without touching each other. If the current in coil A increases with time, in response, the coil B.

 (a) is attracted by A (c) is repelled (c) is repelled (d) rotates
• 2)

Mutual inductance is the phenomenon of inducing emf in a coil, due to a change of current in the neighbouring coil. The amount of mutual inductance that links one coil to another depends very much on the relative positioning of the two coils, their geometry and relative separation between them. Mutual inductance between the two coils increases $\mu_{r}$ times if the coils are wound over an iron core of relative permeability $\mu_{r}$.

(I) A short solenoid of radius a, number of turns per unit length nI' and length L is kept coaxially inside a very long solenoid of radius b, numbdr of turns per unit length n2• What is the mutual inductance of the system?

 $\text { (a) } \mu_{0} \pi b^{2} n_{1} n_{2} L$ $\text { (b) } \mu_{0} \pi a^{2} n_{1} n_{2} L^{2}$ $\text { (c) } \mu_{0} \pi a^{2} n_{1} n_{2} L$ $\text { (d) } \mu_{0} \pi b^{2} n_{1} n_{2} L^{2}$

(ii) If a change in current of 0.01 A in one coil produces a change in magnetic flux of 2 x l0-2 weber in another coil, then the mutual inductance between coils is

 (a) 0 (b) 0.5 H (c) 2 H (d) 3 H

(iii) Mutual inductance of two coils can be increased by

 (a) decreasing the number of turns in the coils (b) increasing the number of turns in the coils (c) winding the coils on wooden cores (d) none of these

(iv) When a sheet of iron is placed in between the two co-axial coils, then the mutual inductance between the coils will

 (a) increase (b) decrease (c) remains same (d) cannot be predicted

(v) The SI unit of mutual inductance is

 (a) ohm (b) mho (c) henry (d) none of these
• 3)

Currents can be induced not only in conducting coils, but also in conducting sheets or blocks. Current is induced in solid metallic masses when the magnetic flux threading through them changes. Such currents flow in the form of irregularly shaped loops throughout the body of the metal. These currents look like eddies or whirlpools in water so they are known as eddy currents. Eddy currents have both undesirable effects and practically useful applications. For example it causes unnecessary heating and wastage of power in electric motors, dynamos and in the cores of transformers.
(I) The working of speedometers of trains is based on

 (a) wattless currents (b) eddy currents (c) alternating currents (d) pulsating currents

(ii) Identify the wrong statement

 (a) Eddy currents are produced in a steady magnetic field (b) Induction furnace uses eddy currents to produce heat. (c) Eddy currents can be used to produce braking force in moving trains (d) Power meters work on the principle of eddy currents.

(iii) Which of the following is the best method to reduce eddy currents?

 (a) Laminating core (b) Using thick wires (c) By reducing hysteresis loss (d) None ofthese

(iv) The direction of eddy currents is given by

 (a) Fleming's left hand rule (b) Biot-Savart law (c) Lenz's law (d) Ampere-circuital law

(v) Eddy currents can be used to heat localised tissues of the human body. This branch of medical therapy is called

 (a) Hyperthermia (b) Diathermy (c) Inductothermy (d) none of these
• 4)

When a current I flows through a coil, flux linked with it is $\phi=L I,$ where L is a constant known as self-inductance of the coil. Any change in current sets up an induced emf in the coil. Thus, self-inductance of a coil is the induced emf set up in it when the current passing through it changes at the unit rate. It is a measure of the opposition to the growth or the decay of current flowing through the coil. Also, value of self-inductance depends on the number of turns in the solenoid, its area of cross-section, and the relative permeability of its core material.

(I) The inductance in a coil plays the same role as

 (a) inertia in mechanics (b) energy in mechanics (c) momentum in mechanics (d) force in mechanics

(ii) A current of 2.5 A flows through a coil of inductance 5 H. The magnetic flux linked with the coil is

 (a) 0.5 Wb (b) 12.5 Wb (c) zero (d) 2 Wb

(iii) The inductance L of a solenoid depends upon its radius R as

 $\text { (a) } L \propto R$ $\text { (b) } L \propto 1 / R$ $\text { (c) } L \propto R^{2}$ $\text { (d) } L \propto R^{3}$

(iv) The unit of self-inductance is

 (a) weber ampere (b) weber-1 ampere (c) ohm second (d) farad

(v) The induced e.m.f in a coil of 10 henry inductance in which current varies from 9 A to 4 A in 0.2 second is

 (a) 200 V (b) 250 V (c) 300 V (d) 350 V
• 5)

In year 1820 Oersted discovered the magnetic effect of current. Faraday gave the thought that reverse of this phenomenon is also possible i.e., current can also be produced by magnetic field. Faraday showed that when we move a magnet towards the coil which is connected by a sensitive galvanometer. The galvanometer gives instantaneous deflection showing that there is an electric current in the loop.
Whenever relative motion between coil and magnet takes place an emf induced in coil. If coil is in closed circuit then current is also induced in the circuit. This phenomenon is called electromagnetic induction.

(I) The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a galvanometer. The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was

 (a) moving towards the solenoid (b) moving into the solenoid (c) at rest inside the solenoid (d) moving out of the solenoid.

(ii) Two similar circular loops carry equal currents in the same direction. On moving the coils further apart, the electric current will

 (a) remain unaltered (b) increases in one and decreases in the second (c) increase in both (d) decrease in both

(iii) A closed iron ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is

 (a) equal to g (b) less than g (c) more than g (d) depends on the diameter of the ring and length of magnet

(iv) Whenever there is a relative motion between a coil and a magnet, the magnitude of induced emf set up in the coil does not depend upon the

 (a) relative speed between the coil and magnet (b) magnetic moment of the coil (c) resistance of the coil (d) number of turns in the coil

(v) A coil of metal wire is kept stationary in a non-uniform magnetic field

 (a) an emf and current both are induced in the coil (b) a current but no emf is induced in the coil (c) an emf but no current is induced in the coil (d) neither emf nor current is induced in the coil

#### Class 12th Physics - Magnetism And Matter Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

The earth's magnetic field at a point on its surface is usually characterised by three quantities: (a) declination (b) inclination or dip and (c) horizontal component of the field. These are known as the elements of the earth's magnetic field. At a place, angle between geographic meridian and magnetic meridian is defined as magnetic declination, whereas angle made by the earth's magnetic field with the horizontal in magnetic meridian is known as magnetic dip.

(i) In a certain place, the horizontal component of magnetic field is $\frac{1}{\sqrt{3}}$ times the vertical component. The angle of dip at this place is

 (a) zero $\text { (b) } \pi / 3$ $\text { (c) } \pi / 2$ $\text { (d) } \pi / 6$

(ii) The angle between the true geographic north and the north shown by a compass needle is called as

 (a) inclination (b) magnetic declination (c) angle of meridian (d) magnetic pole

(iii) The angles of dip at the poles and the equator respectively are

 (a) 30°,60° (b) 0°,90° (c) 45°,90° (d) 90°,0°

(iv) A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It

 (a) will become rigid showing no movement (b) will stay in any position (c) will stay in north-south direction only (d) will stay in east-west direction only.

(v) Select the correct statement from the following

 (a) The magnetic dip is zero at the centre of the earth (b) Magnetic dip decreases as we move away from the equator towards the magnetic pole (c) Magnetic dip increases as we move away from the equator towards the magnetic pole (d) Magnetic dip does not vary-from place to place.
• 2)

By analogy to Gauss's law of electrostatics, we can write Gauss's law of magnetism as $\oint \vec{B} \cdot d \vec{s}=\mu_{0} m_{\text {inside }}$ where $\oint \vec{B} \cdot d \vec{s}$ is the magnetic flux and $m_{\text {inside }}$ is the net pole strength inside the closed surface.
We do not have an isolated magnetic pole in nature. At least none has been found to exist till date. The smallest unit of the source of magnetic field is a magnetic dipole where the net magnetic pole is zero. Hence, the net magnetic pole enclosed by any closed surface is always zero. Correspondingly, the flux of the magnetic field through any closed surface is zero.

(I) Consider the two idealised systems
(i) a parallel plate capacitor with large plates and small separation and
(ii) a long solenoid oflength L >> R, radius of cross-section.
In (i) $\vec{E}$ is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zerq outside. These idealised assumptions, however, contradict fundamental laws as below

 (a) case (i) contradicts Gauss's law for electrostatic fields (b)case (ii) contradicts Gauss's aw for magnetic fields $\text { (c) case (i) agrees with } \oint \vec{E} \cdot \overrightarrow{d l}=0 \text { . }$ $\text { (d) case (ii) contradicts } \oint \vec{H} \cdot \overrightarrow{d l}=I_{e n}$

(ii) The net magnetic flux through any closed surface, kept in a magnetic field is

 (a) zero $\text { (b) } \frac{\mu_{0}}{4 \pi}$ $\text { (c) } 4 \pi \mu_{0}$ $\text { (d) } \frac{4 \mu_{0}}{\pi}$

(iii) A closed surface S encloses a magnetic dipole of magnetic moment 2ml. The magnetic flux emerging from the surface is

 $\text { (a) } \mu_{0} m$ (b) zero $\text { (c) } 2 \mu_{0} m$ $\text { (d) } \frac{2 m}{\mu_{0}}$

(iv) Which of the following is not a consequence of Gauss's law?

 (a) The magnetic poles always exist as unlike pairs of equal strength. (b) If several magnetic lines of force enter in a closed surface, then an equal number of lines of force must leave that surface (c) There are abundant sources or sinks of the magnetic field inside a closed surface (d) Isolated magnetic poles do not exist

(v) The surface integral of a magnetic field over a surface

 (a) is proportional to mass enclosed (b) is proportional to charge enclosed (c) is zero (d) equal to its magnetic flux through that surface.
• 3)

When the atomic dipoles are aligned partially or fully, there is a net magnetic moment in the direction of the field in any small volume of the material. The actual magnetic field inside material placed in magnetic field is the sum of the applied magnetic field and the magnetic field due to magnetisation. This field is called magnetic intensity (H).
$H=\frac{B}{\mu_{0}}-M$
where M is the magnetisation of the material, llo is the permittivity of vacuum and B is the total magnetic field. The measure that tells us how a magnetic material responds to an external field is given by a dimensionless quantity is appropriately called the magnetic susceptibility: for a certain class of magnetic materials, intensity of magnetisation is directly proportional to the magnetic intensity.
(i) Magnetization of a sample is

 (a) volume of sample per unit magnetic moment (b) net magnetic moment per unit volume (c) ratio of magnetic moment and pole strength (d) ratio of pole strength to magnetic moment

(ii) Identify the wrongly matched quantity and unit pair.

 (a) Pole strength Am (b). Magnetic susceptibility dimensionless number (c) Intensity of magnetisation A m-I (d) Magnetic permeability Henry m

(iii) A bar magnet has length- 3 cm, cross-sectional area 2 cm2 and magnetic moment 3 A m2. The intensity of magnetisation of bar magnet is

 $\text { (a) } 2 \times 10^{5} \mathrm{~A} / \mathrm{m}$ $\text { (b) } 3 \times 10^{5} \mathrm{~A} / \mathrm{m}$ $\text { (c) } 4 \times 10^{5} \mathrm{~A} / \mathrm{m}$ $\text { (d) } 5 \times 10^{5} \mathrm{~A} / \mathrm{m}$

(iv) A solenoid has core of a material with relative permeability 500 and its windings carry a current of 1 A. The number of turns of the solenoid is 500 per metre. The magnetization of the material is nearly

 $\text { (a) } 2.5 \times 10^{3} \mathrm{Am}^{-1}$ $\text { (b) } 2.5 \times 10^{5} \mathrm{~A} \mathrm{~m}^{-1}$ $\text { (c) } 2.0 \times 10^{3} \mathrm{~A} \mathrm{~m}^{-1}$ $\text { (d) } 2.0 \times 10^{5} \mathrm{~A} \mathrm{~m}^{-1}$

(v) The relative permeability of iron is 6000. Its magnetic susceptibility is

 (a) 5999 (b) 6001 (c) 6000 x 10-7 (d) 6000 x 107
• 4)

The magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth. The axis of the dipole is presently tilted by approximately 11.3o with respect to the axis of rotation of the earth.

The pole near the geographic North pole of the earth is called the North magnetic pole and the pole near the geographic South pole is called South magnetic pole.
(i) The strength of the earth's magnetic field varies from place to place on the earth's surface, its value being of the order of

 (a) 105 T (b) 10-6T (c) 10-5 T (d) 108 T

(ii) A bar magnet is placed North-South with its North-pole due North. The points of zero magnetic field will be in which direction from centre of magnet?

 (a) North-South (b) East-West (c) North-East and South-West (d) None of these.

(iii) The value of angle of dip is zero at the magnetic equator because on it

 (a) V and H are equal (b) the values of Vand H zero (c) the value of V is zero (d) the value of H is zero .

(iv) The angle of dip at a certain place, where the horizontal and vertical components of the earth's magnetic field are equal, is

 (a) 30° (b) 90° (c) 60° (d) 45°

(v) At a place, angle of dip is 30°. If horizontal component of earth's magnetic field is H, then the total intensity of magnetic field will be

 (a) $\frac{H}{2}$ $\text { (b) } \frac{2 H}{\sqrt{3}}$ $\text { (c) } H \sqrt{\frac{3}{2}}$ (d) 2H
• 5)

The field of a hollow wire with constant current is homageneous
Curves in the graph shown give, as functions of radius distance r, the magnitude B of the magnetic field inside and outside four long wires a, b, c and d, carrying currents that are uniformly distributed across the cross sections of the wires. Overlapping portions of the plots are indicated by double labels.

(i) Which wire has the greatest magnitude of the magnetic field on the surface?

 (a) a (b) b (c) c (d) d

(ii) The current density in a wire a is

 (a) greater than in wire c (b) less than in wire (c) equal to that in wire c (d) not comparable to that of in wire c due to lack of information

(iii) Which wire has the greatest radius?

 (a) a (b) b (c) c (d) d

(iv) A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

 (a) uniform throughout the pipe but not zero (b) zero only along the axis of the pipe (c) zero at any point inside the pipe (d) maximum at the centre and minimum at the edges

(v) In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite direction. The magnetic field is zero

 (a) outside the cable (b) inside the inner conductor (c) inside the outer conductor (d) in between the two conductor.

#### Class 12th Physics - Moving Charges And Magnetism Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

Various methods can be used to measure the mass of an atom. One possibility is through the use of a mass spectrometer. The basic feature of a Banbridge mass spectrometer is illustrated in figure. A particle carrying a charge +q is first sent through a velocity selector and comes out with velocity v = E/B.
The applied electric and magnetic fields satisfy the relation E = vB so that the trajectory of the particle is a straight line. Upon entering a region where a second magnetic field $\vec{B}_{0}$ pointing into the page has been applied, the particle will move in a circular path with radius r and eventually strike the photographic plate.

(i) In mass spectrometer, the ions are sorted out in which of the following ways?

 (a) By accelerating them through electric field (b) By accelerating them through magnetic field (c) By accelerating them through electric and magnetic field (d) By applying a high voltage

(ii) Radius of particle in second magnetic field Bo is

 $\text { (a) } \frac{2 m v}{q E_{0}}$ $\text { (b) } \frac{m v}{q E_{0}}$ $\text { (c) } \frac{m v}{q B_{0}}$ $\text { (d) } \frac{2 m E_{0} v}{q B_{0}}$

(iii) Which of the following will trace a circular trajectory wit largest radius?

 (a) Proton (b) -$\alpha$particle (c) Electron (d) A particle with charge twice and mass thrice that of electron

(iv) Mass of the particle in terms q, Bo, B,r and E is

 $\text { (b) } \frac{q B_{0} B r}{E}$ $\text { (c) } \frac{q B r}{E B_{0}}$ $\text { (d) } \frac{q B r E}{B_{0}}$

(v) The particle comes out of velocity selector along a straight line, because

 (a) electric force is less than magnetic force (b) electric force is greater than magnetic force (c) electric and magnetic force balance each other (d) can't say.
• 2)

Ampere's law gives a method to calculate the magnetic field due to given current distribution. According to it, the circulation $\oint \vec{B} \cdot d \vec{l}$ of the resultant magnetic field along a closed plane curve is equal to $\mu_{0}$ times the total current crossing the area bounded by the closed curve provided the electric field inside the loop remains constant. Ampere's law is more useful under certain symmetrical conditions. Consider one such case of a long Straight wire with circular cross-section (radius R) carrying current I uniformly distributed across this cross-section.

(i) The magnetic field at a radial distance r from the centre of the wire in the region r > R, is

 $\text { (a) } \frac{\mu_{0} I}{2 \pi r}$ $\text { (b) } \frac{\mu_{0} I}{2 \pi R}$ $\text { (c) } \frac{\mu_{0} I R^{2}}{2 \pi r}$ $\text { (d) } \frac{\mu_{0} I r^{2}}{2 \pi R}$

(ii) The magnetic field at a distance r in the region r < R is

 $\text { (a) } \frac{\mu_{0} I}{2 r}$ $\text { (b) } \frac{\mu_{0} I r^{2}}{2 \pi R^{2}}$ $\text { (c) } \frac{\mu_{0} I}{2 \pi r}$ $\text { (d) } \frac{\mu_{0} I r}{2 \pi R^{2}}$

(iii) A long straight wire of a circular cross section (radius a) carries a steady current I and the current I is uniformly distributed across this cross-section. Which of the following plots represents the variation of magnitude of magnetic field B with distance r from the centre of the wire?

(iv) A long straight wire of radius R carries a steady current I. The current is uniformly distributed across its cross-section. The ratio of magnetic field at R/2 and 2R is

 $\text { (a) } \frac{1}{2}$ (b) 2 $\text { (c) } \frac{1}{4}$ (d) 1

(v) A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

 (a) uniform throughout the pipe but not zero (b) zero only along the axis of the pipe (c) zero at any point inside the pipe (d) maximum at the centre and minimum at the edges.
• 3)

The path of a charged particle in magnetic field depends upon angle between velocity and magnetic field.If velocity $\vec{v}$ is at angle $\theta$ to $\vec{B}$ component of velocity parallel to magnetic field $(v \cos \theta)$ remains constant and component of velocity perpendicular to magnetic field $(v \sin \theta)$ is responsible for circular motion, thus the charge particle moves in a helical path.

The plane of the circle is perpendicular to the magnetic field and the axis of the helix is parallel to the magnetic field. The charged particle. moves along helical path touching the line parallel to the magnetic field passing through the starting point after each rotation.
Radius of circular path is $r=\frac{m v \sin \theta}{1 v_{q} B}$
Hence the resultant path of the charged particle will be a helix, with its axis along the direction of $\vec{B}$ as shown in figure.
(i) When a positively charged particle enters into a uniform magnetic field with uniform velocity, its trajectory can be (i) a straight line (ii) a circle (iii) a helix.

 (a) (i) only (b) (i) or (ii) (c) (i) or (iii) (d) anyone of (i), (ii) and (iii)

(ii) Two charged particles A and B having the same charge, mass and speed enter into a magnetic field in such a way that the initial path of A makes an angle of 30° and that of B makes an angle of 90° with the field. Then the trajectory of

 (a) B will have smaller radius of curvature than that of A (b) both will have the same curvature (c) A will have smaller radius of curvature than that of B (d) both will move along the direction of their original velocities.

(iii) An electron having momentum 2.4 x 10-23kg m/ s enters a region of uniform magnetic field of 0.15 T. The field vector makes an angle of 30° with the initial velocity vector of the electron. The radius of the helical path of the electron in the field shall be

 (a) 2 mm (b) 1 mm $\text { (c) } \frac{\sqrt{3}}{2} \mathrm{~mm}$ (d) 0.5 mm

(iv) The magnetic field in a certain region of space is given by $\vec{B}=8.35 \times 10^{-2} \hat{i}$ T. A proton is shot into the field with velocity $\vec{v}=\left(2 \times 10^{5} \hat{i}+4 \times 10^{5} \hat{j}\right) \mathrm{m} / \mathrm{s}$ The proton follows a helical path in the field. The distance moved by proton in the x-direction during the period of one revolution in the yz-plane will be
(Mass of proton = 1.67 x 10-27kg)

 (a) 0.053 m (b) 0.136 m (c) 0.157 m (d) 0.236 m

(v) The frequency of revolution of the particle is

 $\text { (a) } \frac{m}{q B}$ $\text { (b) } \cdot \frac{q B}{2 \pi m}$ $\text { (c) } \frac{2 \pi R}{v \cos \theta}$ $\text { (d) } \frac{2 \pi R}{v \sin \theta}$
• 4)

An electron with speed V<< c moves in a circle ofradius ro in a uniform magnetic field. This electron is able to traverse a circular path as magnetic field is perpendicular to the velocity of the electron. A force acts on the particle perpendicular to both $\vec{v}_{0}$ and $\vec{B}$. This force continuously deflects the particle sideways without  changing its speed and the particle will move along a circle perpendicular to the field. The time required for one revolution of the electron is To .

(i) If the speed of the electron is now doubled to 2vo.The radius of the circle will change to

 $\text { (a) } 4 r_{0}$ $\text { (b) } 2 r_{0}$ $\text { (c) } r_{0}$ $\text { (d) } r_{0} / 2$

(ii) If vo = 2vo then the time required for one revolution of the electron will change to

 $\text { (a) } 4 T_{0}$ $\text { (b) } 2 T_{0}$ $\text { (c) } T_{0}$ $\text { (d) } T_{0} / 2$

(iii) A charged particles is projected in a magnetic field $\vec{B}=(2 \hat{i}+4 \hat{j}) \times 10^{2} \mathrm{~T}$ The acceleration of the particle is found to be $\vec{a}=(x \hat{i}+2 \hat{j}) \mathrm{m} \mathrm{s}^{-2}$. Find the value of x.

 (a) 4 m S-2 (b) -4 m s-2 (c) -2 m s-2 (d) 2 m s-2

(iv) If the given electron has a velocity not perpendicular to B, then trajectory of the electron is

 (a) straight line (b) circular (c) helical (d) zig-zag

(v) If this electron of charge (e) is moving parallel to uniform magnetic field with constant velocity v, the force acting on the electron is

 (a) Bev $\text { (b) } \frac{B e}{v}$ $\text { (c) } \frac{B}{e v}$ (d) zero
• 5)

When a rectangular loop PQRS of sides 'a' and 'b' carrying current I is placed in uniform magnetic field $\vec{B}$ such that area vector $\vec{A}$ makes an angle $\theta$ with direction of magnetic field, then forces on the arms QR and SP of loop are equal, opposite and collinear, thereby perfectly cancel each other, whereas forces on the arms PQ and RS of loop are equal and opposite but not collinear, so they give rise to torque on the loop.

Force on side PQ or RS ofloop is F = IbB sin 90° = Ib B and perpendicular distance between two non-collinear forces is $r_{\perp}$ = a sin $\theta$

So, torque on the loop, $\tau=I A B \sin \theta$
In vector form torque $\vec{\tau}=\vec{M} \times \vec{B}$
where $\vec{M}=N I \vec{A}$ is called magnetic dipole moment of current loop and is directed in direction of area vector $\vec{A}$ i.e., normal to the plane ofloop.
(i) A circular loop of area 1 cm2, carrying a current of 10 A is placed in a magnetic field of 0.1 T perpendicular to the plane of the loop. The torque on the loop due to the magnetic field is

 (a) zero (b) 10-4 N m (c) 10-2 N m (d) 1N m

(ii) Relation between magnetic moment and angular velocity is

 $\text { (a) } M \propto \omega$ $\text { (b) } M \propto \omega^{2}$ $\text { (c) } M \propto \sqrt{\omega}$ (d) none of these

(ill) A current loop in a magnetic field

 (a) can be in equilibrium in two orientations, both the equilibrium states are unstable (b) can be in equilibrium in two orientations, one stable while the other is unstable (c) experiences a torque whether the field is uniform or non uniform in all orientations (d) can be in equilibrium in one orientation

(iv) The magnetic moment of a current I carrying circular coil of radius r and number of turns N varies as

 $\text { (a) } \frac{1}{r^{2}}$ $\text { (b) } \frac{1}{r}$ (c) r (d) r2

(v) A rectangular coil carrying current is placed in a non-uniform magnetic field. On that coil the total

 (a) force is non-zero (b) force is zero (c) torque is zero (d) none of these

(i) (c): In mass spectrometer, the ions are sorted
out by accelerating them through electric and magnetic
field.

#### Class 12th Physics - Electrostatic Potential And Capacitance Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

Electrostatic potential energy of a system of point charges is defined as the total amount of work done in bringing the different charges to their respective positions from infinitely charge mutual separations. The work is stored in the system of two point charges in the form of electrostatic potential energy U of the system. Electric potential difference between any points A and B in an electric field is the amount of work done in moving a unit positive test charge from A to B along any path agents the electrostatic force
$V_{B}-V_{A}=\frac{W_{A B}}{q_{0}}=\int \mid \vec{E} \cdot d l$

(i) A test charge is moved from lower potential point to a higher potential point. The potential energy of test charge will

 (a) remain the same (b) increase (c) decrease (d) become zero

(ii) Which of the following statement is not true?

 (a) Electrostatic force is a conservative force. (b) Potential energy of charge q at a point is the work done per unit charge in bringing a charge from any point to infinity (c) Spring force and gravitational force are conservative force. (d) Both (a) and (c).

(iii) Work done in moving a charge from one point to another inside a uniformly charged conducting sphere is

 (a) always zero (b) non-zero (c) maybe zero (d) none of these

(iv) The work done in bringing a unit positive charge from infinite distance to a point at distance x from a positive charge Q is W. Then the potential $\phi$ at that point is

 $\text { (a) } \frac{W Q}{x}$ (b) W $\text { (c) } \frac{W}{x}$ (d) WQ

(v) If $1 \mu C$ charge is shifted from A to B and it is found that work done by an external force is $40 \mu \mathrm{J}$In doing so against electrostatics force, the potential difference VA- VB is

 (a) 40 V (b) -40 V (c) 20 V (d) -60 V
• 2)

Potential difference ($\Delta$V) between two points A and B separated by a distance x, in a uniform electric field E is given by $\Delta V=-E x$,where x is measured parallel to the field lines. If a charge qo moves from P to Q, the changein potential energy $(\Delta U)$ is given as $\Delta U=q_{0} \Delta V .$ A proton is released from rest in uniform electric field of magnitude $4.0 \times 10^{8} \mathrm{Vm}^{-1}$ directed along the positive X-axis. The proton undergoes a displacement of 0.25 m in the direction of E.
Mass of a proton = 1.66 x 10-27 kg and charge of proton = 1.6 x10-19 C

(i) The change in electric potential of the proton between the points A and B is

 $\text { (a) }-1 \times 10^{8} \mathrm{~V}$ $\text { (b) } 1 \times 10^{8} \mathrm{~V}$ $\text { (c) } 6.4 \times 10^{-19} \mathrm{~V}$ $\text { (d) }-6.4 \times 10^{-19} \mathrm{~V}$

(ii) The change in electric potential energy of the proton for displacement from A to B is

 $\text { (a) } 1.6 \times 10^{11} \mathrm{~J}$ $\text { (b) } 0.5 \times 10^{23} \mathrm{~J}$ $\text { (c) }-1.6 \times 10^{-11} \mathrm{~J}$ $\text { (d) } 3.2 \times 10^{22} \mathrm{~J}$

(iii) The mutual electrostatic potential energy between two protons which are at a distance of 9 x 10-15 m, in ${ }_{92} \mathrm{U}^{235}$ nucleus is

 $\text { (a) } 1.56 \times 10^{-14} \mathrm{~J}$ $\text { (b) } 5.5 \times 10^{-14} \mathrm{~J}$ $\text { (c) } 2.56 \times 10^{-14} \mathrm{~J}$ $\text { (d) } 4.56 \times 10^{-14} \mathrm{~J}$

(iv) If a system consists of two charges 4 mC and -3mC with no external field placed at (-5 em, 0, 0) and (5 em, 0, 0) respectively. The amount of work required to separate the two charges infinitely away from each other is

 (a) -1.1 J (b) 2 J (c) 2.5 J (d) 3 J

(v) As the proton moves from P to Q, then

 (a) the potential energy of proton decreases (b) the potential energy of proton increases (c) the proton loses kinetic energy (d) total energy of the proton increases
• 3)

The potential at any observation point P of a static electric field is defined as the work done by the external agent (or negative of work done by electrostatic field) in slowly bringing a unit positive point charge from infinity to the observation point. Figure shows the potential variation along the line of charges. Two point charges Q1 and Q2 lie along a line at a distance from each other.

(i) At which of the points 1, 2 and 3 is the electric field is zero?

 (a) 1 (b) 2 (c) 3 (d) Both (a) and (b)

(ii) The signs of charges Q1 and Q2 respectively are

 (a) positive and negative (b) negative and positive (c) positive and positive (d) negative and negative

(iii) Which of the two charges Q1 and Q2 is greater in magnitude?

 (a) Q2 (b) Q1 (c) Same (d) Can't determined

(iv) Which of the following statement is not true?

 (a) Electrostatic force is a conservative force (b) Potential energy of charge q at a point is the work done per unit charge in bringing a charge from any point to infinity (c) When two like charges lie infinite distance apart, their potential energy is zero. (d) Both (a) and (c).

(v) Positive and negative point charges of equal magnitude are kept at $\left(0,0, \frac{a}{2}\right)$ and $\left(0,0, \frac{-a}{2}\right)$ respectively.
The work done by the electric field when another positive point charge is moved from (-a, 0, 0) to (0, a, 0) is

 (a) positive (b) negative (c) zero (d) depends on the path connecting the initial and final positions
• 4)

For the various charge systems, we represent equipotential surfaces by curves and line of force by full line curves. Between any two adjacent equipotential surfaces, we assume a constant potential difference the equipotential surfaces of a single point charge are concentric spherical shells with their centres at the point charge. As the lines of force point radially outwards, so they are perpendicular to the equipotential surfaces at all points.

(i) Identify the wrong statement.

 (a) Equipotential surface due to a single point charge is spherical. (b) Equipotential surface can be constructed for dipoles too. (c) The electric field is normal to the equipotential surface through the point. (d) The work done to move a test charge on the equipotential surface is positive

(ii) Nature of equipotential surface for a point charge is

 (a) Ellipsoid with charge at foci (b) Sphere with charge at the centre of the sphere (c) Sphere with charge on the surface of the sphere (d) Plane with charge on the surface

(iii) A spherical equipotential surface is not possible

 (a) inside a uniformly charged sphere (b) for a dipole (c) inside a spherical condenser (d) for a point charge

(iv) The work done in carrying a charge q once round a circle of radius a with a charge Q at its centre is

 $\text { (a) } \frac{q Q}{4 \pi \varepsilon_{0} a}$ $\text { (b) } \frac{q Q}{4 \pi \varepsilon_{0} a^{2}}$ $\text { (c) } \frac{q}{4 \pi \varepsilon_{0} a}$ (d) zero

(v) The work done to move a unit charge along an equipotential surface from P to Q

 (a) must be defined as $-\int_{P}^{Q} \vec{E} \cdot d \vec{l}$ (b) is zero (c) can have a non-zero value (d) both (a) and (b) are correct
• 5)

This energy possessed by a system of charges by virtue of their positions. When two like charges lie infinite distance apart, their potential energy is zero because no work has to be done in moving one charge at infinite distance from the other.
In carrying a charge q from point A to point B, work done $W=q\left(V_{A}-V_{B}\right)$. This work may appear as change in KE/PE of the charge. The potential energy of two charges q1and q2 at a distance r in air is $\frac{q_{1} q_{2}}{4 \pi \varepsilon_{0} r}$.It is measured in joule. It may be positive, negative or zero depending on the signs of ql and q2.
(i) Calculate work done in separating two electrons form a distance of 1 m to 2 m in air, where e is electric charge and k is electrostatic force constant.

 (a) ke2 (b) e2/2 (c) -ke2/2 (d) zero

(ii) Four equal charges q each are placed at four corners of a square of side a each. Work done in carrying a charge -q from its centre to infinity is

 (a) zero $\text { (b) } \frac{\sqrt{2} q^{2}}{\pi \varepsilon_{0} a}$ $\text { (c) } \frac{\sqrt{2} q}{\pi \varepsilon_{0} a}$ $\text { (d) } \frac{q^{2}}{\pi \varepsilon_{0} a}$

(iii) Two points A and B are located in diametrically opposite directions of a point charge of +2 $\mu \mathrm{C}$ at distances 2 m and 1 m respectively from it. The potential difference between A and B is

 (a) 3 x 103 V (b) 6 x 104 V (c) -9 X 103 V (d) -3 x 103 V

(iv) Two point charges A = +3 nC and B = +1 nC are placed 5 ern apart in air. The work done to move charge B towards A by 1 cm is

 (a) 2.0 x 10-7 J (b) 1.35 x 10-7 J (c) 2.7 X 10-7 J (d) 12.1 x 10-7 J

(v) A charge Q is placed at the origin. The electric potential due to this charge at a given point in space is V.The work done by an external force in bringing another charge q from infinity up to the point is

 $\text { (a) } \frac{V}{q}$ (b) Vq (c) V + q (d) V

#### Class 12th Physics - Current Electricity Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

The flow of charge in a particular direction constitutes the electric current. Current is measured in Ampere. Quantitatively, electric current in a conductor across an area held perpendicular to the direction of flow of charge is defined as the amount of charge is flowing across that area per unit time.
Current density at a point in a conductor is the ratio of the current at that point in the conductor to the area of cross section of the conductor of that point.
The given figure shows a steady current flows in a metallic conductor of non uniform cross section. Current density depends inversely on area, so, here $J_{1}>J_{2}, \text { as } A_{1}<A_{2}$.

(i) What is the current flowing through a conductor, if one million electrons are crossing in' one millisecond through a cross-section of it ?

 (a) 2.5 x 10-10 A (b) 1.6 x 10-10 A (c) 7.5 X 10-9 A (d) 8.2 x 10-11 A

(ii) SI unit of electric current is

 (a) Cs (b) Ns-2 (c) Cs-1 C-1s-1

(iii) A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor?

 (a) Electric field (b) Drift velocity (c) Current (d) Current density

(iv) A constant current I is flowing along the length of a conductor of variable cross-section as shown in the figure. The quantity which does not depend upon the area of cross-section is

 (a) electron density (b) current density (c) drift velocity (d) electric field

(v) When a current of 40 A flows through a conductor of area 10 m2, then the current density is

 (a) 4 A/m2 (b) 1 A/m2 (c) 2 A/m2 (d) 8 A/m2
• 2)

According to Ohm's law, the current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor i.e $I \propto V \Rightarrow \frac{V}{I}=R$ where R is resistance of the conductor Electrical resistance of a conductor is the obstruction posed by the conductor to the flow of electric current through it. It depends upon length, area of cross-section, nature of material and temperature of the conductor We can write $R \propto \frac{l}{A} \text { or } R=\rho \frac{l}{A}$ where $\rho$ is electrical resistivity of the material of the conductor.
(i) Dimensions of electric resistance is

 $\text { (a) }\left[\mathrm{ML}^{2} \mathrm{~T}^{-2} \mathrm{~A}^{-2}\right]$ $\text { (b) }\left[M L^{2} T^{-3} A^{-2}\right]$ $\text { (c) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-2} \mathrm{~T}^{-1} \mathrm{~A}\right]$ $\text { (d) }\left[M^{-1} L^{2} T^{2} A^{-1}\right]$

(ii) If $1 \mu \mathrm{A}$ current flows through a conductor when potential difference of2 volt is applied across its ends, then the resistance of the conductor is

 $\text { (a) } 2 \times 10^{6} \Omega$ $\text { (b) } 3 \times 10^{5} \Omega$ $\text { (c) } 1.5 \times 10^{5} \Omega$ $\text { (d) } 5 \times 10^{7} \Omega$

(iii) Specific resistance of a wire depends upon

 (a) length (b) cross-sectional area (c) mass (d) none of these

(iv) The slope of the graph between potential difference and current through a conductor is

 (a) a straight line (b) curve (c) first curve then straight line (d) first straight line then curve

(v) The resistivity of the material of a wire 1.0 m long, 0.4 mm in diameter and having a resistance of 2.0 ohm is

 $\text { (a) } 1.57 \times 10^{-6} \Omega \mathrm{m}$ $\text { (b) } 5.25 \times 10^{-7} \Omega \mathrm{m}$ $\text { (c) } 7.12 \times 10^{-5} \Omega \mathrm{m}$ $\text { (d) } 2.55 \times 10^{-7} \Omega \mathrm{m}$
• 3)

The resistance of a conductor at temperature toC is given by R= Ro (1 + $\alpha$t)
where Rt is the resistance at toC, Ro is the resistance at 0oC and $\alpha$ is the characteristics constants of the material of the conductor.
Over a limited range of temperatures, that is not too large. The resistivity of a metallic conductor is approximately given by $\rho_{t}=\rho_{0}(1+\alpha t)$.
where $\alpha$ is the temperature coefficient of resistivity. Its unit is $\mathrm{K}^{-1} \text {or }{ }^{\circ} \mathrm{C}^{-1}$
For metals, $\alpha$ is positive i.e., resistance increases with rise in temperature.
For insulators and semiconductors, $\alpha$ is negative i.e., resistance decreases with rise in temperature.

(i) Fractional increase in resistivity per unit increase in temperature is defined as

 (a) resistivity (b) temperature coefficient of resistivity (c) conductivity (d) drift velocity

(ii) The material whose resistivity is insensitive to temperature is

 (a) silicon (b) copper (c) silver (d) nichrome

(iii) The temperature coefficient of the resistance of a wire is 0.00125 per oC. At 300 K its resistance is 1 ohm. The resistance of wire will be 2 ohms at

 (a) 1154 K (b) 1100 K (c) 1400 K (d) 1127 K

(iv) The temperature coefficient of resistance of an alloy used for making resistors is

 (a) small and positive (b) small and negative (c) large and positive (d) large and negative

(v) For a metallic wire, the ratio V/I (V = applied potential difference and I = current flowing) is

 (a) independent of temperature (b) increases as the temperature rises (c) decreases as the temperature rises (d) increases or decreases as temperature rises depending upon the metal
• 4)

Emf of a cell is the maximum potential difference between two electrodes of the cell when no current is drawn from the cell. Internal resistance is the resistance offered by the electrolyte of a cell when the electric current flows through it. The internal resistance of a cell depends upon the following factors;
(i) distance between the electrodes
(ii) nature and temperature of the electrolyte
(iii) nature of electrodes
(iv) area of electrodes.

For a freshly prepared cell, the value of internal resistance is generally low and goes on increasing as the cell is put to more and more use. The potential difference between the two electrodes of a cell in a closed circuit is called terminal potential difference and its value is always less than the emf of the cell in a closed circuit. It can be written as V = E - Jr.
(i) The terminal potential difference of two electrodes of a cell is equal to emf of the cell when

 $\text { (a) } I \neq 0$ (b) I=0 (c) both (a) and (b) (d) neither (a)nor (b)

(ii) A cell of emf E and internal resistance r gives a current of 0.5 A with an external resistance of $12 \Omega$ and a current of 0.25 A with an external resistance of $25 \Omega$ .What is the value of internal resistance of the cell?

 $\text { (a) } 5 \Omega$ $\text { (b) } 1 \Omega$ $\text { (c) } 7 \Omega$ $\text { (d) } 3 \Omega$

(iii) Choose the wrong statement.

 (a) Potential difference across the terminals of a cell in a closed circuit is always less than its emf. (b) Internal resistance of a cell decrease with the decrease in temperature of the electrolyte. (c) Potential difference versus current graph for a cell is a straight line with a -ve slope (d) Terminal potential difference of the cell when it is being charged is given as V = E + Ir.

(iv) An external resistance R is connected to a cell of internal resistance r, the maximum current flows in the external resistance, when

 (a) R = r (b) R < r (c) R> r (d) R=l/r

(v) IF external resistance connected to a cell has been increased to 5 times, the potential difference across the terminals of the cell increases from 10 V to 30 V. Then, the emf of the cell is

 (a) 30 V (b) 60V (c) 50 V (d) 40 V
• 5)

Metals have a large number of free electrons nearly 1028 per cubic metre. In the absence of electric field, average  terminal speed of the electrons in random motion atroom temperature is of the order of 105 m s-1When a potential difference V is applied across the two ends of a given conductor, the free electrons in the conductor experiences a force and are accelerated towards the positive end of the conductor. On their way, they suffer frequent collisions with the ions/atoms of the conductor and lose their gained kinetic energy. After each collision, the free electrons are again accelerated due to electric field, towards the positive end of the conductor and lose their gained kinetic energy in the next collision with the ions/atoms of the conductor. The average speed of the free electrons with which they drift towards the positive end of the conductor under the effect of applied electric field is called drift speed of the electrons.
(i) Magnitude of drift velocity per unit electric field is

 (a) current density (b) current (c) resistivity (d) mobility

(ii) The drift speed of the electrons depends on

 (a) dimensions of the conductor (b) number density of free electrons in the conductor (c) both (a) and (b) (d) neither (a) nor (b)

(iii) We are able to obtain fairly large currents in a conductor because

 (a) the electron drift speed is usually very large (b) the number density of free electrons is very high and this can compensate for the low values of the 6 electron drift speed and he very small magnitude of the electron charge (c) the number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge (d) the very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed to get the electric current

(iv) Drift speed of electrons in a conductor is very small i.e., i = 10-4 m s-1. The Electric bulb glows immediately. When the switch is closed because

 (a) drift velocity of electron increases when switch is closed (b) electrons are accelerated towards the negative end of the conductor (c) the drifting of electrons takes place at the entire length of the conductor (d) the electrons of conductor move towards the positive end and protons of conductor move towards negative end of the conductor

(v) The number density offree electrons in a copper conductor is 8.5 x 1028 m-3. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 x 10-6m2 and it is carrying a current of 3.0 A.

 (a) 8.1 x 104 s (b) 2.7 x 104 s (c) 9 x 103 s (d) 3 x 103 S

#### Class 12th Physics - Electric Charges And Fields Case Study Questions and Answers 2022 - 2023 - by Study Materials - View & Read

• 1)

Coulomb's law states that the electrostatic force of attraction or repulsion acting between two stationary point charges is given by
$F=\frac{1}{4 \pi \varepsilon_{0}} \frac{q_{1} q_{2}}{r^{2}}$

where F denotes the force between two charges q1 and qseparated by a distance r in free space, Eo is a constant known as permittivity of free space. Free space is vacuum and may be taken to be air practically.
If free space is replaced by a medium, then Eo is replaced by (Eok) or (EoEr)where k is known as dielectric constant or relative permittivity.
(i) In coulomb's law, F = $k \frac{q_{1} q_{2}}{r^{2}}$, then on which of the following factors does the proportionality constant k depends?

 (a) Electrostatic force acting between the two charges (b) Nature of the medium between the two charges (c) Magnitude of the two charges (d) Distance between the two charges

(ii) Dimensional formula for the permittivity constant Eof free space is

 $\text { (a) }\left[\mathrm{ML}^{-3} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]$ $\text { (b) }\left[M^{-1} L^{3} T^{2} A^{2}\right]$ $\text { (c) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-3} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]$ $\text { (d) }\left[M L^{-3} T^{4} A^{-2}\right]$

(iii) The force of repulsion between two charges of 1 C each, kept 1 m apart in vaccum is

 $\text { (a) } \frac{1}{9 \times 10^{9}} \mathrm{~N}$ $\text { (b) }\left[M^{-1} L^{3} T^{2} A^{2}\right]$ $\text { (c) } 9 \times 10^{7} \mathrm{~N}$ $\text { (d) } \frac{1}{9 \times 10^{12}} \mathrm{~N}$

(iv) Two identical charges repel each other with a force equal to 10 mgwt when they are 0.6 m apart in air. (g = 10 ms-2). The value of each charge is

 (a) 2 mC (b) 2 x10-7 mC (c) 2 nC (d) 2$\mu$C

(v) Coulomb's law for the force between electric charges most closely resembles with

 (a) law of conservation of energy (b) Newton's law of gravitation (c) Newton's 2nd law of motion (d) law of conservation of charge
• 2)

Smallest charge that can exist in nature is the charge of an electron. During friction it is only the transfer of electrons which makes the body charged. Hence net charge on any body is an integral multiple of charge of an electron.

[1.6 x 10-19 C] i.e.
q = ± ne
where n = 1,2,3,4, ....
Hence no body can have a charge represented as $1.1 e, 2.7 e, \frac{3}{5} e, \text { etc. }$
Recently, it has been discovered that elementary particles such as protons or neutrons are composed of more elemental units called quarks.
(i) Which of the following properties is not satisfied by an electric charge?

 (a) Total charge conservation (b) Quantization of charge (c) Two types of charge (d) Circular line of force

(ii) Which one of the following charges is possible?

 (a) 5.8 x 10-18C (b) 3.2 x 10-18C (c) 4.5 x 10-19C (d) 8.6 x 10-19C

(iii) If a charge on a body is 1 nC, then how many electrons are present on the body?

 (a) 6.25 x 1027 (b) 1.6 x 1019 (c) 6.25 x 1028 (d) 6.25 x 109

(iv) If a body gives out 109 electrons every second, how much time is required to get a total charge of 1 C from it?

 (a) 190.19 years (b) 150.12 years (c) 198.19 years (d) 188.21 years

(v) A polythene piece rubbed with wool is found to have a negative charge of3.2 x 1O-7C.Calculate the number of electrons transferred.

 (a) 2 x 1012 (b) 3 x 1012 (c) 2 x 1014 (d) 3 x 1014
• 3)

Net electric flux through a cube is the sum of fluxes through its six faces. Consider a cube as shown in figure,having sides oflength L = 10.0 cm. The electric field is uniform, has a magnitude E = 4.00 x 103 N C-I and is parallel to the xy plane at an angle of 37° measured from the +x-axis towards the +y-axis.

(i) Electric flux passing through surface S6 is

 (a) -24 N m2 C-1 (b) 24 N m2 C-1 (c) 32 Nm2C-1 (d) -32 N m2 C-1

(ii) Electric flux passing through surface s1 is

 (a) -24 N m2 C-1 (b) 24 N m2 C-1 (c) 32 N m2 C-1 (d) -32 N m2 C-1

(iii) The surfaces that have zero flux are

 (a) S1 and S3 (b) S5 and S6 (c) S2 and S4 (d) S1 and S2

(iv) The total net electric flux through all faces of the cube is

 (a) 8 N m2 C-1 (b) -8 N m2 C-1 (c) 24 N m2 C-1 (d) zero

(v) The dimensional formula of surface integral $\oint \vec{E} \cdot d \vec{S}$of an electric field is

 (a) [M L2 T-2 A-1] (b) [M L3 T-3 A-1] (c) [M-1 L3 T-3 A] (d) [M L-3 T-3 A-1]
• 4)

When a charged particle is placed in an electric field, it experiences an electrical force. If this is the only force on the particle, it must be the net force. The net force will cause the particle to accelerate according to Newton's second law. So
$\vec{F}_{e}=q \vec{E}=m \vec{a}$

If $\vec{E}$ is uniform, then $\vec{a}$ is constant and $\vec{a}=q \vec{E} / m$. If the particle has a positive charge, its acceleration is in the direction of the field. If the particle has a negative charge, its acceleration is in the direction opposite to the electric field. Since the acceleration is constant, the kinematic equations can be used.
(i) An electron of mass m, charge e falls through a distance h metre in a uniform electric field E. Then time of fall,

 $\text { (a) } t=\sqrt{\frac{2 h m}{e E}}$ $\text { (b) } t=\frac{2 h m}{e E}$ $\text { (c) } t=\sqrt{\frac{2 e E}{h m}}$ $\text { (d) } t=\frac{2 e E}{h m}$

(ii) An electron moving with a constant velocity v along X-axis enters a uniform electric field applied along Y-axis. Then the electron moves.

 (a) with uniform acceleration along Y-axis (b) without any acceleration along Y-axis (c) in a trajectory represented as y = ax2 (d) in a trajectory represented as y = ax

(iii) Two equal and opposite charges of masses ml and m2 are accelerated in an uniform electric field through the same distance. What is the ratio of their accelerations if their ratio of masses is $\frac{m_{1}}{m_{2}}=0.5 ?$

 $\text { (a) } \frac{a_{1}}{a_{2}}=2$ $\text { (b) } \frac{a_{1}}{a_{2}}=0.5$ $\text { (c) } \frac{a_{1}}{a_{2}}=3$ $\text { (d) } \frac{a_{1}}{a_{2}}=1$

(iv) A particle of mass m carrying charge q is kept at rest in a uniform electric field E and then released. The kinetic energy gained by the particle, when it moves through a distance y is

 $\text { (a) } \frac{1}{2} q E y^{2}$ $\text { (b) } q E y$ $\text { (c) } q E y^{2}$ $\text { (d) } q E^{2} y$

(v) A charged particle is free to move in an electric field. It will travel

 (a) always along a line of force (b) along a line of force, if its initial velocity is zero (c) along a line of force, if it has some initial velocity in the direction of an acute angle with the line of force (d) none of these.
• 5)

In 1909, Robert Millikan was the first to find the charge of an electron in his now-famous oil-drop experiment. In that experiment, tiny oil drops were sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops were observed with a magnifying eyepiece, and the electric field was adjusted so that the upward force on some negatively charged oil drops was just sufficient to balance the downward force of gravity. That is, when suspended, upward force qE just equaled Mg. Millikan accurately measured the charges on many oil drops and found the values to be whole number multiples of 1.6 x 10-19 C the charge of the electron. For this, he won the Nobel prize.

(i) If a drop of mass 1.08 x 10-14 kg remains stationary in an electric field of 1.68 x 105 N C-I, then the charge of this drop is

 (a) 6.40 x 10-19 C (b) 3.2 x 10-19 C (c) 1.6 X 10-19 C (d) 4.8 x 10-19 C

(ii) Extra electrons on this particular oil drop (given the presently known charge of the electron) are

 (a) 4 (b) 3 (c) 5 (d) 8

(iii) A negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field 100 V m-1.If the mass of the drop is 1.6 X 10-3 g, the number of electrons carried by the drop is (g= 10 m s-2)

 (a) 1018 (b) 1015 (c) 1012 (d) 109

(iv) The important conclusion given by Millikan's experiment about the charge is

 (a) charge is never quantized (b) charge has no definite value (c) charge is quantized (d) charge on oil drop always increases.

(v) If in Millikan's oil drop experiment, charges on drops are found to be $8 \mu \mathrm{C}, 12 \mu \mathrm{C}, 20 \mu \mathrm{C}$ then quanta of charge is

 $\text { (a) } 8 \mu \mathrm{C}$ $\text { (b) } 20 \mu \mathrm{C}$ $\text { (c) } 12 \mu \mathrm{C}$ $\text { (d) } 4 \mu \mathrm{C}$

#### CBSE 12th Standard Physics Subject Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

In Pradeep's classroom, the fan was running very slowly. Due to which, his teacher was sweating and was restless and tired.All his classmates wanted to rectify this. They called an electrician who came and changed the capacitor only, after which the fan started running fast.
Answer the following questions based on the above information:
(i) What energy is stored in the capacitor and where?
(ii) A thin metal sheet is placed in the middle of a parallel plate capacitor. What will be the effect on the capacitance?
(iii) What values did the classmates have?

• 2)

When an electric dipole of moment $\left| P \right|$ = q $\times$ 2a is held at an angle $\theta$, with the direction of uniform external electric field E, a torque $\tau$ = pE sin$\theta$ acts on the dipole. This torque tries to align the electric dipole in the direction of the field. When p is along E, $\theta=0^{o}$$\tau$ = pE sin$0^{o}$ = zero.

(i) What is the direction of torque acting on an electric dipole held at a angle with uniform external field?
(ii) An electric dipole of length 10 cm having charge $\pm 6\times { 10 }^{ -3 }$, C placed at $30^{o}$ with respect to a uniform electric field experiences a torque of magnitude $6\sqrt { 3 }$ N-m. Calculate magnitude of electric field.
(iii) What is the physical significance of this concept in our day-today life?

• 3)

The surface integral of electrostatic field E produced by any source over any closed surface S enclosing a volume V in vacuum, i.e. total electric flux over the closed surface S in vacuum is $1/{\epsilon}_{0}$ times the total charge Q contained inside S, i.e.
${\phi}_{E}=\oint E.dS={{Q}\over{{\epsilon}_{0}}}$
The charges inside S may be point charges or even continuous charge distributions. There is no contribution to "total electric flux from the charges outside S. Further, the location of Q inside S does not affect the value of surface integral.
What are the SI units and dimensions of electric flux?
A closed surface in vacuum encloses charges - q, + 3 q and +5 q. Another charge + 4 q lies outside the surface. What is total electric flux over the surface?
A point charge a lies inside a spherical surface of radius r. How will the electric flux be affected, if, radius of the sphere is doubled?
What values of life do you learn from this theorem?

• 4)

Vishwajeet purchased cells for his transistor. He felt that cells are not working properly. He wanted to check their emf. So, he took the cells to the physics lab and with the help of potentiometer found their emf. To his surprise, emf was less than the value claimed by the manufacturer. He lodged the complaint with consumer forum and received the deserving response.
(i) What values are displayed by Vishwajeet?
(ii) Why do you think Vishwajeet used potentiometer instead of voltmeter to find out emf of the cell? For more precise measurement, the potential gradient of the potentiometer should be high or low?

• 5)

Saniya and Priya are friends. Both of them know that a small compass needle point always along north-south direction. One day Saniya is plotting field due to a bar magnet in the laboratory. She discovers a point where compass needle does not point along N-S. Rather, it sets itself in any arbitrary direction. Saniya thinks first that compass needle has become faulty. Priya then explains to her the real situation.
(i) How did Priya justify the situation?
(ii) If a bar magnet is placed along the N-S direction with its north pole pointing north, what is the position of neutral points?
(iii) If a bar magnet is placed along N-S direction with its north pole pointing South, What is the position of neutral points?
(iv) What values of life do you learn from this piece of knowledge?

#### CBSE 12th Standard Physics Subject Value Based Questions 5 Mark Questions 2021 Part - II - by Sharma - Kochi - View & Read

• 1)

A rectangular coil of n turns each of area A, carrying current I, when suspended in a uniform magnetic field B, experiences a torque
$\tau =nI \ BA \ sin\theta$
Where is $\theta$ the angle which a normal drawn on the plane of coil makes with the direction of magnetic field. This torque tends to rotate the coil and bring it in an equilibrium position. In the stable equilibrium state, the resultant force on the coil is zero. The torque on the coil is also zero and the coil has minimum potential energy.
(i) In which position, a current carrying coil suspended in uniform magnetic field experiences (a) minimum torque and (b) maximum torque?
(ii) a circular coil of 200 turns, radius 5 cm carries a current of 2.0 A. It is suspended vertically in a uniform horizontal magnetic field of 0.20 T, with the plane of the coil making an angle with $60°$ the field lines. Calculate the magnitude of the torque that must be applied on it to prevent it from turning.
(iii) what is the basic value displayed by the above study?

• 2)

That night Vaikunth was preparing for his physics exam. Suddenly, the light in his room went off and he could not continue his studies. His cousin brother Vasu who had come to visit him was quick to react. Vasu using the torch (an android application) installed in his mobile phone found that the fuse had blown out. He checked the wiring and located a short circuit. He checked the wiring and located a short circuit. He rectified it and put a fuse wire. The light came to life again. Vaikunth had a sign of releif and continued his studies.
(i) What are the values projected by Vaikunth and Vasu?
(ii) Why did Vasu have to check the wiring?
(iii) What is an electric fuse? What characteristics you would prefer for a fuse wire?

• 3)

Two linear parallel conductors carrying currents in the same direction attract each other and two linear parallel conductors carrying in opposite directions repel each other. The force acting per unit length due to currents ${ I }_{ 1 }and{ I }_{ 2 }$in two linear parallel conductors held distance r apart in vacuum in SI unit is $F=\frac { { \mu }_{ 0 } }{ 2\pi } \frac { 2{ I }_{ 1 }{ I }_{ 2 } }{ r }$
(i) What is the basic reason for the force between two linear parallel conductors currents?
(ii) Two straight wires A and B of lengths 2 cm and 20 cm, carrying currents  2.0 A and 5.0 A respectively in opposite directions are lying parallel to each other 4.0 cm apart. The wire A is held near the middle of wire B. What is the force on 20 cm long wire B?
(iii) What does this study imply in day to day life?

• 4)

Self- inductance is the property of a coil by virtue of which the coil oppose any change in the strength of current flowing through it by inducing an emf in itself. The induced emf is also called back emf. Self-inductance represents electric inertia which is measured in terms of coefficient of self-inductance(L). We can show that
L =  $L=\cfrac { \phi }{ I }$ = $\cfrac { -e }{ { \triangle I }/{ \triangle t } }$
(i) How does the self-inductance of a coil represent its electric inertia?
(ii) An emf of 100$\mu$ V is induced in a coil when the current in it changes from 5A to 1A in 0.4s.
Find the self-inductance of the coil.

• 5)

Raj is in XII standard. His Physics teacher demonstrated an experiment to explain Faraday's laws of electromagnetic induction. Raj interrupted his lecture and asked, "Is there any possibility of induced emf due to the earth's magnetism"? The teacher was stunned for a moment and gave this question for group discussion. Finally, the students came out with correct answer.
(i) Write the values that you learnt from this incident.
(ii) What can be reason for Raj's question?

#### CBSE 12th Standard Physics Subject Moving Charges And Magnetism HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - View & Read

• 1)

Equal currents I=2A are flowing through the infinitely long wires parallel to Y-axis located at x=+1m, x=+2m, x=+4m and so on, but in opposite directions as shown in figure. Find the magnetic field at the origin O.

• 2)

One alpha particle and a deuteron entered perpendicularly in a uniform magnetic field with same velocity. Which one follow the greater circle?

• 3)

A charge particle moving in a magnetic field penetrates a layer of lead and thereby losses half of its kinetic energy. How does the radius of curvature of its path change?

• 4)

You are given a copper wire carrying current I of length L. Now the wire is turned into circular coil. Find the number of turns in the coil so that the torque at the centre of the coil is to maximum

• 5)

In an exercise to increase current sensitivity of a galvanometer by 25 % , its resisitance is increased by 1.5 times . How does the voltage sensititvity of the galvanometer be affected

#### CBSE 12th Standard Physics Subject Current Electricity HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - View & Read

• 1)

when is more power delivered to a light bulb, just after it is turned on and the glow of the filament is increasing or after it has been ON for a few seconds and the glow is steady?

• 2)

A cell of emf E and internal resistance r is connected across a variabl resistor R. Plot a graph showing variation terminal voltage V of the cell versus the current I. Using the plot, show how emf of the cell and its internal resistance can be determined.

• 3)

Use Kirchhoff,s rules to determine the potential difference between the points A and D. When no current flows in the arm BE of the electric network shown in the figure below.

• 4)

AB is a potentiometer wire as shown in figure. If the value of R is increased, in which direction will the balance point J shift?

• 5)

Three resistance 3Ω,6Ω and 9Ω are connected to a battery. In which of them will the power dissipation be maximum if a) They are all connected in parallel b) They are all connected in series Give reason.

#### CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 2 Mark Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

For faster action which transistor is used and why?

• 2)

A germanium diode is preferred to a silicon one for rectifying small voltages. Explain why?

• 3)

Express by a truth table the output Y for all possible inputs A and B in the circuit shown below

• 4)

Write the Boolean equation and truth table for the circuit shown below.What is the output when all the inputs are high?

• 5)

Construct AND gate using NAND GATE and give its truth table

#### CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - View & Read

• 1)

In the working of a transistor, emitter-base junction is forward biased while collector-base junction is reverse biased. Why?

• 2)

In normal case, emitter-base junction is the forward bias and collector-base junction is reverse biased. What will happen if emitter is reverse biased and collector is forward biased?

• 3)

Two car generates have a common gate which needs to open automatically when a car enters either of the garages or cars enter both. A circuit, that resembles this situation using diodes for this situation.

• 4)

A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5 V and it has to regulate voltage which fluctuated between 3 V and 7 V, what should be the value of RS for safe operations as shown below figure?

• 5)

Give a brief explanation that how a NOT gate is realised Using NAND gate.

#### CBSE 12th Standard Physics Subject Wave Optics HOT Questions 2 Mark Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

An onject AB is kept in front of a concave mirror as shown in the figure.

Complete the ray diagram showing the image formation of the object.

• 2)

When monochromatic light travels from a rarer to a denser medium, explain the following, giving reasons.
(i) Is the frequency of reflected and refracted light same as the frequency of incident light?
(ii) Does the decrease in speed imply a reduction in the energy carried light wave?

• 3)

In the given figure, for what value of (For prism, $\mu$=1.524

• 4)

Two convex lenses of same focal but of aperture lenses in twp astronomical telescope having the identical eyepeice. What is the ratio of their resolving power? Which telescope will you prefer and why? Give reason.

• 5)

Find an expression for intensity of transmitted light, when a polaroid sheet is rotated between two crossed polaroids. In which position of the polaroid sheet will thw transmitted intensity be maximum?

#### CBSE 12th Standard Physics Subject Wave Optics HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - View & Read

• 1)

Can we increase the range of a telescope by increasing the diameter of the objective lens?

• 2)

A man stands in front of a mirror of special shape.He finds that his image has a very small head, a fat body and legs of normal size.What can you say about the shapes of three parts of the mirror?

• 3)

For the same angle of incidence, the angles of refraction in media P, Q and R are $35°,25°,15°$ resp.In which medium will the velocity of light be minimum?

• 4)

A lens whose radii of curvature are different is forming the image of an object placed on its axis.If the lens is reversed, will the position of the image change?

• 5)

Is Huygens' principle valid for longitundinal sound waves?

#### CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance HOT Questions 2 Mark Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

A square surface of side l metre is in the plane of paper. A uniform electric field E (volt/metre), also in the plane of the paper, is limited only to the lower half of the square surface, (see figure). What is the electric flux associated with this surface?

• 2)

A thin fixed ring of radius 2 m has a positive charge of 10-6C uniformly distributed over it. A particle of mass 0.9 g and having a negative charge 10-7C is placed on the axis at a distance of 2cm from the center of the ring. Show that motion of the negatively charged particle is approximately SHM. Calculate the time period of oscillation.

• 3)

A charged Particle q is shot towards another charged particle Q which is fixed , with a speed v. It approaches Q up to a closet distance r and then returns, If q were given a speed 2 v the n find the closet distance of approach.

• 4)

Two Capacitors of capacitace 6$\mu$F and 12$\mu$F ae connnected in series with tha battery the volatage across the 6$\mu$F capacitor is 2 volt, Compute the total battery voltage.

• 5)

An electric dipole is held in an uniform electric field. Using suitable diagram, show at it doesn't undergo any translatory motion, and (ii) derive an expression for torque acting on it and specify its direction.

#### CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - View & Read

• 1)

A charged Particle is free to move in an electric field.Will it always move along an electric line of force ?

• 2)

A 2 m insulating slab with a large aluminum sheet of area 1m2 on its top is fixed by a man outside his house one evening. Will he get an electric shock, if he touches the metal sheet next morning?

• 3)

Guess a possible reason, why water has a much greater dielectric constant (= 80) than mica (= 6)?

• 4)

A technician has only two capacitors. By using them in series or in parallel, he is able to obtain the capacitance of 4, 5, 20 and 25 $\mu$ F. What is the capacitance of both capacitors?

• 5)

A and B have identical size and same mass. A becomes A2+ and B become B2- . Will A2+ and B2- still have the same mass? Why?

#### CBSE 12th Standard Physics Subject Communication Systems HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

A schematic arrangement for transmitting a message signal (20 Hz to 20kHz) is given below:

Give two drawbacks from which this arrangement suffers. Describe briefly with the help of a block diagram the alternative arrangement for the transmission and reception of the message signal

• 2)

The TV transmission tower at a particular place has a height of 160m. What is its coverage range? By how much should the height be increased to double its coverage range? Given that radius of earth = 6400 km

• 3)

A TV tower has a height of 110m. How much population is covered by the TV broadcast if the average population density around the tower is 1000 km-2? Given that radius of Earth = 6.4 x 106m

• 4)

A microwave telephone link operating at the cenral frequency of 10 GHz has been established .If 2 % of this is available for microwave communication channel, then how many telephones channels can be simultaneously granted if each telephone is allotted a band width of 8 KHz

• 5)

You are given three semiconductors A,B,C with respective band gaps of 3eV, 2eV and 1eV for use in a photodetector to detect $\lambda$ = 1400nm . Select the suitable semiconductor. Give reasons

#### CBSE 12th Standard Physics Subject Communication Systems HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - View & Read

• 1)

How are side bands produced?

• 2)

Why are microwave considered better carriers of signals than ratio waves?

• 3)

In the given diagram C(t) stands for the carrier wave and m(t) for the signal to be transmitted. What name do we give to the wave labelled as Cm(t) in the diagram?

• 4)

The carrier wave is given by   C(t) = 2 sin $(8\pi t)$ volt. The modulating signal is a square wave as shown. Find modulation index.

• 5)

Why are micro wave used in radars?

#### CBSE 12th Standard Physics Subject Magnetism And Matter Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

The earth's magnetic field at a point on its surface is usually characterised by three quantities: (a) declination (b) inclination or dip and (c) horizontal component of the field. These are known as the elements of the earth's magnetic field. At a place, angle between geographic meridian and magnetic meridian is defined as magnetic declination, whereas angle made by the earth's magnetic field with the horizontal in magnetic meridian is known as magnetic dip.

(i) In a certain place, the horizontal component of magnetic field is $\frac{1}{\sqrt{3}}$ times the vertical component. The angle of dip at this place is

 (a) zero $\text { (b) } \pi / 3$ $\text { (c) } \pi / 2$ $\text { (d) } \pi / 6$

(ii) The angle between the true geographic north and the north shown by a compass needle is called as

 (a) inclination (b) magnetic declination (c) angle of meridian (d) magnetic pole

(iii) The angles of dip at the poles and the equator respectively are

 (a) 30°,60° (b) 0°,90° (c) 45°,90° (d) 90°,0°

(iv) A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It

 (a) will become rigid showing no movement (b) will stay in any position (c) will stay in north-south direction only (d) will stay in east-west direction only.

(v) Select the correct statement from the following

 (a) The magnetic dip is zero at the centre of the earth (b) Magnetic dip decreases as we move away from the equator towards the magnetic pole (c) Magnetic dip increases as we move away from the equator towards the magnetic pole (d) Magnetic dip does not vary-from place to place.
• 2)

By analogy to Gauss's law of electrostatics, we can write Gauss's law of magnetism as $\oint \vec{B} \cdot d \vec{s}=\mu_{0} m_{\text {inside }}$ where $\oint \vec{B} \cdot d \vec{s}$ is the magnetic flux and $m_{\text {inside }}$ is the net pole strength inside the closed surface.
We do not have an isolated magnetic pole in nature. At least none has been found to exist till date. The smallest unit of the source of magnetic field is a magnetic dipole where the net magnetic pole is zero. Hence, the net magnetic pole enclosed by any closed surface is always zero. Correspondingly, the flux of the magnetic field through any closed surface is zero.

(I) Consider the two idealised systems
(i) a parallel plate capacitor with large plates and small separation and
(ii) a long solenoid oflength L >> R, radius of cross-section.
In (i) $\vec{E}$ is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zerq outside. These idealised assumptions, however, contradict fundamental laws as below

 (a) case (i) contradicts Gauss's law for electrostatic fields (b)case (ii) contradicts Gauss's aw for magnetic fields $\text { (c) case (i) agrees with } \oint \vec{E} \cdot \overrightarrow{d l}=0 \text { . }$ $\text { (d) case (ii) contradicts } \oint \vec{H} \cdot \overrightarrow{d l}=I_{e n}$

(ii) The net magnetic flux through any closed surface, kept in a magnetic field is

 (a) zero $\text { (b) } \frac{\mu_{0}}{4 \pi}$ $\text { (c) } 4 \pi \mu_{0}$ $\text { (d) } \frac{4 \mu_{0}}{\pi}$

(iii) A closed surface S encloses a magnetic dipole of magnetic moment 2ml. The magnetic flux emerging from the surface is

 $\text { (a) } \mu_{0} m$ (b) zero $\text { (c) } 2 \mu_{0} m$ $\text { (d) } \frac{2 m}{\mu_{0}}$

(iv) Which of the following is not a consequence of Gauss's law?

 (a) The magnetic poles always exist as unlike pairs of equal strength. (b) If several magnetic lines of force enter in a closed surface, then an equal number of lines of force must leave that surface (c) There are abundant sources or sinks of the magnetic field inside a closed surface (d) Isolated magnetic poles do not exist

(v) The surface integral of a magnetic field over a surface

 (a) is proportional to mass enclosed (b) is proportional to charge enclosed (c) is zero (d) equal to its magnetic flux through that surface.
• 3)

When the atomic dipoles are aligned partially or fully, there is a net magnetic moment in the direction of the field in any small volume of the material. The actual magnetic field inside material placed in magnetic field is the sum of the applied magnetic field and the magnetic field due to magnetisation. This field is called magnetic intensity (H).
$H=\frac{B}{\mu_{0}}-M$
where M is the magnetisation of the material, llo is the permittivity of vacuum and B is the total magnetic field. The measure that tells us how a magnetic material responds to an external field is given by a dimensionless quantity is appropriately called the magnetic susceptibility: for a certain class of magnetic materials, intensity of magnetisation is directly proportional to the magnetic intensity.
(i) Magnetization of a sample is

 (a) volume of sample per unit magnetic moment (b) net magnetic moment per unit volume (c) ratio of magnetic moment and pole strength (d) ratio of pole strength to magnetic moment

(ii) Identify the wrongly matched quantity and unit pair.

 (a) Pole strength Am (b). Magnetic susceptibility dimensionless number (c) Intensity of magnetisation A m-I (d) Magnetic permeability Henry m

(iii) A bar magnet has length- 3 cm, cross-sectional area 2 cm2 and magnetic moment 3 A m2. The intensity of magnetisation of bar magnet is

 $\text { (a) } 2 \times 10^{5} \mathrm{~A} / \mathrm{m}$ $\text { (b) } 3 \times 10^{5} \mathrm{~A} / \mathrm{m}$ $\text { (c) } 4 \times 10^{5} \mathrm{~A} / \mathrm{m}$ $\text { (d) } 5 \times 10^{5} \mathrm{~A} / \mathrm{m}$

(iv) A solenoid has core of a material with relative permeability 500 and its windings carry a current of 1 A. The number of turns of the solenoid is 500 per metre. The magnetization of the material is nearly

 $\text { (a) } 2.5 \times 10^{3} \mathrm{Am}^{-1}$ $\text { (b) } 2.5 \times 10^{5} \mathrm{~A} \mathrm{~m}^{-1}$ $\text { (c) } 2.0 \times 10^{3} \mathrm{~A} \mathrm{~m}^{-1}$ $\text { (d) } 2.0 \times 10^{5} \mathrm{~A} \mathrm{~m}^{-1}$

(v) The relative permeability of iron is 6000. Its magnetic susceptibility is

 (a) 5999 (b) 6001 (c) 6000 x 10-7 (d) 6000 x 107
• 4)

The magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth. The axis of the dipole is presently tilted by approximately 11.3o with respect to the axis of rotation of the earth.

The pole near the geographic North pole of the earth is called the North magnetic pole and the pole near the geographic South pole is called South magnetic pole.
(i) The strength of the earth's magnetic field varies from place to place on the earth's surface, its value being of the order of

 (a) 105 T (b) 10-6T (c) 10-5 T (d) 108 T

(ii) A bar magnet is placed North-South with its North-pole due North. The points of zero magnetic field will be in which direction from centre of magnet?

 (a) North-South (b) East-West (c) North-East and South-West (d) None of these.

(iii) The value of angle of dip is zero at the magnetic equator because on it

 (a) V and H are equal (b) the values of Vand H zero (c) the value of V is zero (d) the value of H is zero .

(iv) The angle of dip at a certain place, where the horizontal and vertical components of the earth's magnetic field are equal, is

 (a) 30° (b) 90° (c) 60° (d) 45°

(v) At a place, angle of dip is 30°. If horizontal component of earth's magnetic field is H, then the total intensity of magnetic field will be

 (a) $\frac{H}{2}$ $\text { (b) } \frac{2 H}{\sqrt{3}}$ $\text { (c) } H \sqrt{\frac{3}{2}}$ (d) 2H
• 5)

The field of a hollow wire with constant current is homageneous
Curves in the graph shown give, as functions of radius distance r, the magnitude B of the magnetic field inside and outside four long wires a, b, c and d, carrying currents that are uniformly distributed across the cross sections of the wires. Overlapping portions of the plots are indicated by double labels.

(i) Which wire has the greatest magnitude of the magnetic field on the surface?

 (a) a (b) b (c) c (d) d

(ii) The current density in a wire a is

 (a) greater than in wire c (b) less than in wire (c) equal to that in wire c (d) not comparable to that of in wire c due to lack of information

(iii) Which wire has the greatest radius?

 (a) a (b) b (c) c (d) d

(iv) A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

 (a) uniform throughout the pipe but not zero (b) zero only along the axis of the pipe (c) zero at any point inside the pipe (d) maximum at the centre and minimum at the edges

(v) In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite direction. The magnetic field is zero

 (a) outside the cable (b) inside the inner conductor (c) inside the outer conductor (d) in between the two conductor.

#### CBSE 12th Standard Physics Subject Moving Charges And Magnetism Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - View & Read

• 1)

Ampere's law gives a method to calculate the magnetic field due to given current distribution. According to it, the circulation $\oint \vec{B} \cdot d \vec{l}$ of the resultant magnetic field along a closed plane curve is equal to $\mu_{0}$ times the total current crossing the area bounded by the closed curve provided the electric field inside the loop remains constant. Ampere's law is more useful under certain symmetrical conditions. Consider one such case of a long Straight wire with circular cross-section (radius R) carrying current I uniformly distributed across this cross-section.

(i) The magnetic field at a radial distance r from the centre of the wire in the region r > R, is

 $\text { (a) } \frac{\mu_{0} I}{2 \pi r}$ $\text { (b) } \frac{\mu_{0} I}{2 \pi R}$ $\text { (c) } \frac{\mu_{0} I R^{2}}{2 \pi r}$ $\text { (d) } \frac{\mu_{0} I r^{2}}{2 \pi R}$

(ii) The magnetic field at a distance r in the region r < R is

 $\text { (a) } \frac{\mu_{0} I}{2 r}$ $\text { (b) } \frac{\mu_{0} I r^{2}}{2 \pi R^{2}}$ $\text { (c) } \frac{\mu_{0} I}{2 \pi r}$ $\text { (d) } \frac{\mu_{0} I r}{2 \pi R^{2}}$

(iii) A long straight wire of a circular cross section (radius a) carries a steady current I and the current I is uniformly distributed across this cross-section. Which of the following plots represents the variation of magnitude of magnetic field B with distance r from the centre of the wire?

(iv) A long straight wire of radius R carries a steady current I. The current is uniformly distributed across its cross-section. The ratio of magnetic field at R/2 and 2R is

 $\text { (a) } \frac{1}{2}$ (b) 2 $\text { (c) } \frac{1}{4}$ (d) 1

(v) A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

 (a) uniform throughout the pipe but not zero (b) zero only along the axis of the pipe (c) zero at any point inside the pipe (d) maximum at the centre and minimum at the edges.
• 2)

An electron with speed V<< c moves in a circle ofradius ro in a uniform magnetic field. This electron is able to traverse a circular path as magnetic field is perpendicular to the velocity of the electron. A force acts on the particle perpendicular to both $\vec{v}_{0}$ and $\vec{B}$. This force continuously deflects the particle sideways without  changing its speed and the particle will move along a circle perpendicular to the field. The time required for one revolution of the electron is To .

(i) If the speed of the electron is now doubled to 2vo.The radius of the circle will change to

 $\text { (a) } 4 r_{0}$ $\text { (b) } 2 r_{0}$ $\text { (c) } r_{0}$ $\text { (d) } r_{0} / 2$

(ii) If vo = 2vo then the time required for one revolution of the electron will change to

 $\text { (a) } 4 T_{0}$ $\text { (b) } 2 T_{0}$ $\text { (c) } T_{0}$ $\text { (d) } T_{0} / 2$

(iii) A charged particles is projected in a magnetic field $\vec{B}=(2 \hat{i}+4 \hat{j}) \times 10^{2} \mathrm{~T}$ The acceleration of the particle is found to be $\vec{a}=(x \hat{i}+2 \hat{j}) \mathrm{m} \mathrm{s}^{-2}$. Find the value of x.

 (a) 4 m S-2 (b) -4 m s-2 (c) -2 m s-2 (d) 2 m s-2

(iv) If the given electron has a velocity not perpendicular to B, then trajectory of the electron is

 (a) straight line (b) circular (c) helical (d) zig-zag

(v) If this electron of charge (e) is moving parallel to uniform magnetic field with constant velocity v, the force acting on the electron is

 (a) Bev $\text { (b) } \frac{B e}{v}$ $\text { (c) } \frac{B}{e v}$ (d) zero
• 3)

A magnetic field can be produced by moving, charges or electric currents. The basic equation governing the magnetic field due to a current distribution is the Biot-Savart law.
Finding the magnetic field resulting from a current distribution involves the vector product, and is inherently a calculas problem when the distance from the current to the field point is continuously changing.
According to this law, the magnetic field at a point due to a current element oflength $d \vec{l}$ carrying current I, at a distance r from the element is $d B=\frac{\mu_{0}}{4 \pi} \frac{I(d \vec{l} \times \vec{r})}{r^{3}}$
Biot -Savart law has certain similarities as well as difference with Coloumbs law for electrostatic field e.g., there is an angle dependence in Biot-Savart law which is not present in electrostatic case.
(i) The direction of magnetic field $d \vec{B}$ due to a current element $I d \vec{l}$ at a point of distance $\vec{r}$ from it, when a current I passes through a long conductor is in the direction

 $\text { (a) of position vector } \vec{r} \text { of the point }$ $\text { (b) of current element } d \vec{l}$ $\text { (c) perpendicular to both } d \vec{l} \text { and } \vec{r}$ $\text { (d) perpendicular to } d \vec{l} \text { only }$

(ii) The magnetic field due to a current in a straight wire segment of length L at a point on its perpendicular bisector at a distance r (r >> L)

 $\text { (a) decreases as } \frac{1}{r} \text { . }$ $\text { (b) decreases as } \frac{1}{r^{2}} \text { . }$ $\text { (c) decreases as } \frac{1}{r^{3}} \text { . }$ $\text { (d) approaches a finite limit as } r \rightarrow \infty$

(iii) Two long straight wires are set parallel to each other. Each carries a current i in the same direction and the separation between them is 2r. The intensity of the magnetic field midway t between them is

 $\text { (a) } \mu_{0} i / r$ $\text { (b) } 4 \mu_{0} i / r$ (c) zero $\text { (d) } \mu_{0} i / 4 r$

(iv) A long straight wire carries a current along the z-axis for any two points in the x - y plane. Which of the following is always false?

 (a) The magnetic fields are equal (b) The directions of the magnetic fields are the same (c) The magnitudes ofthe magnetic fields are equal (d) The field at one point is opposite to that at the other point

(v) Biot-Savart law can be expressed alternatively as

 (a) Coulomb's Law (b) Ampere's circuital law (c) Ohm's Law (d) Gauss's Law
• 4)

Moving coil galvanometer operates on Permanent Magnet Moving Coil (PMMC) mechanism and was designed by the scientist D'arsonval.
Moving coil galvanometers are of two types
(i) Suspended coil
(ii) Pivoted coil type or tangent galvanometer.
Its working is based on the fact that when a current carrying coil is placed in a magnetic field, it experiences a torque. This torque tends to rotate the coil about its axis of suspension in such a way that the magnetic flux passing through the coil is maximum.

(i) A moving coil galvanometer is an instrument which

 (a) is used to measure emf (b) is used to measure potential difference (c) is used to measure resistance (d) is a deflection instrument which gives a deflection when a current flows through its coil

(ii) To make the field radial in a moving coil galvanometer

 (a) number of turns of coil is kept small (b) magnet is taken in the form of horse-shoe (c) poles are of very strong magnets (d) poles are cylindrically cut

(iii) The deflection in a moving coil galvanometer is

 (a) directly proportional to torsional constant of spring (b) directly proportional to the number of turns in the coil (c) inversely proportional to the area of the coil (d) inversely proportional to the current in the coil

(iv) In a moving coil galvanometer, having a coil of N-turns of area A and carrying current I is placed in a radial field of strength B.
The torque acting on the coil is

 $\text { (a) } N A^{2} B^{2} I$ $\text { (b) } N A B I^{2}$ $\text { (c) } N^{2} A B I$ (d) NABI

(v) To increase the current sensitivity of a moving coil galvanometer, we should decrease

 (a) strength of magnet (b) torsional constant of spring (c) number ofturns in coil (d) area of coil
• 5)

A charged particle moving in a magnetic field experiences a force that is proportional to the strength of the magnetic field, the component of the velocity that is perpendicular to the magnetic field and the charge of the particle.
This force is given by $\vec{F}=q(\vec{v} \times \vec{B})$ where q is the electric charge of the particle, v is the instantaneous velocity of the particle, and B is the magnetic field (in tesla).
The direction of force is determined by the rules of cross product of two vectors
Force is perpendicular to both velocity and magnetic field. Its direction is same as $\vec{v} \times \vec{B}$ if q is positive and opposite of $\vec{v} \times \vec{B}$ if q is negative
The force is always perpendicular to both the velocity of the particle and the magnetic field that created it. Because the magnetic force is always perpendicular to the motion, the magnetic field can do no work on an isolated charge. It can only do work indirectly, via the electric field generated by a changing magnetic field.

(I) When a magnetic field is applied on a stationary electron, it

 (a) remains stationary (b) spins about its own axis (c) moves in the direction of the field (d) moves perpendicular to the direction of the field.

(ii) A proton is projected with a uniform velocity v along the axis of a current carrying solenoid, then

 (a) the proton will be accelerated along the axis (b) the proton path will be circular about the axis (c) the proton moves along helical path (d) the proton will continue to move with velocity v along the axis.

(iii) A charged particle experiences magnetic force in the presence of magnetic field. Which of the following statement is correct?

 (a) The particle is stationary and magnetic field is perpendicular. (b) The particle is moving and magnetic field is perpendicular to the velocity (c) The particle is stationary and magnetic field is parallel (d) The particle is moving and magnetic field is parallel to velocity

(iv) A charge q moves with a velocity 2 ms-1 along x-axis in a uniform magnetic field $\vec{B}=(\hat{i}+2 \hat{j}+3 \hat{k}) \mathrm{T}$ then charge will experience a force

 (a) in z-y plane (b) along -yaxis (c) along +z axis (d) along -z axis

(v) Moving charge will produce

 (a) electric field only (b) magnetic field only (c) both electric and magnetic field (d) none ofthese.

#### un 1 physics - by Sri Krish International School - View & Read

• 1)

Electric field intensity (E) due to an electric dipole varies with distance (r) of the point from the centre of dipole as:

• 2)

The correct relation between electric intensity E and electric potential V is

• 3)

A closed surface in vacuum encloses charges -q and +3q. Another charge -2q lies outside the surface. Total electric flux over the surface is

• 4)

The electric field at a point is

• 5)

Dipole moment is a ............... quantity and its units are .............

#### 12th Standard CBSE Physics Public Model Question Paper IV 2020 - by Sharma - Kochi - View & Read

• 1)

When two capacitors charged to different potentials are connected by a conducting wire, what is not true?

• 2)

A circular current loop of magnetic moment M is in arbitrary orientation in an external magnetic field.$\overset { \rightarrow }{ B }$ The work does to rotate the loop by $30°$about an axis perpendicular to its plane is

• 3)

Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?

• 4)

In an electromagnetic wave, electric and magnetic fields are 200 V/m and 0.365 A/m. The maximum rate of energy flow is

• 5)

How much work is done in moving a 500$\mu C$ charge between two points on an equipotential surface?

#### 12th Standard CBSE Physics Public Model Question Paper III 2020 - by Sharma - Kochi - View & Read

• 1)

The electric field at a point is

• 2)

S is the surface of a lump of magnetic material.

• 3)

A metal plate is getting heated. It can be because

• 4)

The kinetic energy of a photon of frequency v, rest mass.${ m }_{ 0 }$ having mass m while moving with velocity v is

• 5)

How is dielectric constant expressed in terms of capacitance of a capacitor ?

#### 12th Standard CBSE Physics Public Model Question Paper II 2020 - by Sharma - Kochi - View & Read

• 1)

When a number of capacitors are connected in parallel between two points, the equivalent capacitance

• 2)

A long straight wire of radius a carries a steady current i. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at a/2 and 2 a is

• 3)

A wire of length 2m moves with a speed of 5m/s perpendicular to a magnetic field of induction 0.1 Wb/m2. The e.m.f. induced in the wire is

• 4)

The total e.m. power of the sun is

• 5)

The torque acting on an electric dipole of moment p held at an angle $\theta$ with an electric field E is ............

#### 12th Standard CBSE Physics Public Model Question Paper I 2020 - by Sharma - Kochi - View & Read

• 1)

1 stat-Coulomb = ......... Coulomb

• 2)

Two identical current carrying coaxial loops, carry current I in an opposite sense. A simple American loop passes through both of them once. Calling the loop as C,

• 3)

Q factor of resonance is given by

• 4)

Which of the following statements about electromagnetic waves is/are correct
(1) X-rays in vacuum travel faster than light waves in vacuum
(2) The energy of x-rays photon is greater than that of a light photon
(3) light can be polarised by x-rays cannot

• 5)

The test charge used to measure electric field at a point should be vanishingly small.Why?

#### 12th Standard CBSE Physics Public Model Question Paper V 2019 - 202 - by Sharma - Kochi - View & Read

• 1)

Electric field due to an electric dipole is

• 2)

A magnet with moment M is given. If it is bent into a semicircular form, its new magnetic moment will be :

• 3)

The mutual inductance M12 of coil 1 with respect to coil 2

• 4)

A flood light is covered with a filter that transmits red light. The electric field of the emerging beam is represented by a sinusoidal wave.
${ E }_{ x }=36 \ sin\quad (1.20\times { 10 }^{ 7 }z=3.6\times { 10 }^{ 15 }t) \ V/m$
the average intensity of the beam is watt/${ (metre) }^{ 2 }$ will be:

• 5)

Does the charge given to a metallic sphere depend on whether it is hollow or solid? Give reason for your answer.

#### 12th Standard CBSE Physics Public Model Question Paper IV 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

Force $\overrightarrow { F }$ acting on a test charge q in a uniform electric field $\overrightarrow { E }$ is

• 2)

In a cyclotron a charged particle

• 3)

Out of the following, choose the correct relation

• 4)

An EM wave of intensity I falls on a surface kept in vacuum and experts radiation pressure kept in vacuum and experts radiation pressure p on it. Which of the following are true?

• 5)

Two electrically charged particles, having charges of different magnitudes, when placed at a distance 'd' from each other, experience a force of attraction 'F'. These two particles are put in contact and again placed at the same distance from each other. What is the nature of new force between them? Is the magnitude of the force of interaction between them now more or less than F ?

#### 12th Standard CBSE Physics board Exam Model Question Paper III 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region

• 2)

In a cyclotron a charged particle

• 3)

A transformer is an electric device used for

• 4)

The electric field intensity produced by the radiations coming from 100 W bulb at a 3m distance is E. The electric field intensity produced by the radiations coming from 50w bulb at the same distance is:

• 5)

A spherical shell of radius b with charge Q is expanded to a radius a. Find the work done by the electrical forces in the process.

#### 12th Standard CBSE Physics board Exam Model Question Paper II 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

When air inbetween the plates of a capacitor is replaced by mica of dielectric constant 6, its capacity

• 2)

The magnetic field at a perpendicular distance of 2 cm from an infinite straight current carrying conductor is 2x10-6 T. The current in the wire is

• 3)

The relation $\frac { { E }_{ s } }{ { E }_{ p } } =\frac { { n }_{ s } }{ { n }_{ p } }$ is applied only to

• 4)

In an electromagnetic wave, the electric and magnetic fields are 100 V/m and 0.265 A/m. The maximum energy flow per second per unit area will be

• 5)

Why is electrostatic potential constant throught the volume of the conductor and has the same value (as inside) on its surface?

#### 12th Standard CBSE Physics board Exam Model Question Paper I 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

The value of absolute electrical permittivity of free space is

• 2)

In a permanent magnet at room temperature

• 3)

A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. This can be because

• 4)

A linearly polarized electromagnetic wave given as $E={ E }_{ 0 }\overset { \wedge }{ i } cos \ (kz-wt)$ incident wall at $z=a$ . Assuming that the material of the wall os optically inactive, the reflected wave will be given as

• 5)

What is electric field intensity inside a cavity of a conductor kept in an electric field?

#### 12th Standard CBSE Physics Public Model Question Paper IV 2020 - by Sharma - Kochi - View & Read

• 1)

The dimensional formula of electric flux is

• 2)

The value of absolute electrical permittivity of free space is

• 3)

A circular current loop of magnetic moment M is in arbitrary orientation in an external magnetic field.$\overset { \rightarrow }{ B }$ The work does to rotate the loop by $30°$about an axis perpendicular to its plane is

• 4)

Two particles X and Y having equal charges after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii ${ R }_{ 1 }\quad and\quad { R }_{ 2 }$ respectively. The ratio of the mass of X to that Y is

• 5)

The output of a step-down transformer is measured to be 24V when connected to a 12 watt light blub. The value of the peak current is

#### 12th Standard CBSE Physics Public Model Question Paper III 2020 - by Sharma - Kochi - View & Read

• 1)

The SI unit of electric field intensity is

• 2)

Which of the following is not an insulator?

• 3)

A current carrying circular loop of radius R is placed in the x-y plane with centre at the origin. Half of the loop with x>0 is now bent so that it now lies in the y-z plane.

• 4)

A magnetic needle suspended parallel to a magnetic field requires $\sqrt { 3 } J$ of work to turn it through ${ 60 }^{ ° }.$ The torque needed to maintain the needle in this position will be :

• 5)

For an LCR circuit, the power transferred from the driving source to the driven oscillator from the driving source tothe driven oscillator is P = I2Z cos $\phi$.

#### 12th Standard CBSE Physics Public Model Question Paper II 2020 - by Sharma - Kochi - View & Read

• 1)

Electric field due to a single charge is

• 2)

When an electric dipole is held at an angle in a uniform electric field, the net force F and torque $\tau$ on the dipole are

• 3)

If a copper wire carries a direct current, the magnetic field associated with the current will be

• 4)

Two circular coils 1 and 2 are made from the same wire but the radius of the Ist coil twice that of the 2nd coil. What potential difference ratio should be applied across them so that the magnetic field at their centres is the same?

• 5)

The power factor of an a.c. circuit is given by cos $\phi$=

#### 12th Standard CBSE Physics Public Model Question Paper I 2020 - by Sharma - Kochi - View & Read

• 1)

The dimensional formula of electric flux is

• 2)

If $\oint _{ s }^{ }{ E.ds } =0$ over a surface, then

• 3)

A long straight wire of radius a carries a steady current i. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at a/2 and 2 a is

• 4)

A galvanometer having a coil resistance of $100\Omega$ gives a full scale deflection, when a current of 1 mA is passed through it. The value of the resistance, which can convert this galvanometer into ammeter giving a full scale deflection for a current of 10 A is

• 5)

Phase difference between voltage across L and C in series is

#### 12th Standard CBSE Physics Public Model Question Paper V 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

When an electric dipole is held at an angle in a uniform electric field, the net force F and torque $\tau$ on the dipole are

• 2)

What is not true?

• 3)

A circular coil carrying current behaves as a

• 4)

Two similar coils of radius R, are lying concentrically with their planes at right angles to each other. The currents flowing in them are I and 2 I respectively. The resultant magnetic field at the centre will be :

• 5)

The frequency of a.c. generated depends on

#### 12th Standard CBSE Physics Public Model Question Paper IV 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

Charge on a body which carries 200 excess electrons is

• 2)

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region

• 3)

In a cyclotron a charged particle

• 4)

A charged particle would continue to move with a constant velocity in a region wherein,

• 5)

In  a uniform magnetic field of induction B, a wire in the form of semicirclr of radius r rotates about the diameter of the circle with angulat frequency . The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R, then the mean power generated per period of rotation is

#### 12th Standard CBSE Physics Public Model Question Paper III 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

Force $\overrightarrow { F }$ acting on a test charge q in a uniform electric field $\overrightarrow { E }$ is

• 2)

The correct relation between electric intensity E and electric potential V is

• 3)

Ampere's circuital law can be derived from

• 4)

In a cyclotron a charged particle

• 5)

The cause of induced e.m.f. is

#### 12th Standard CBSE Physics Public Model Question Paper II 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

When two capacitors charged to different potentials are connected by a conducting wire, what is not true?

• 2)

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region

• 3)

The magnetic field of earth can be modeled by that of a point dipole placed at the center of the earth. The dipole axis makes an angle of $11.3°$with the axis of the earth. At Mumbai, declination is nearly zero. Then,

• 4)

Two particles each of mass m and charge q are attached to the two ends of a light rigid rod of length 2 R. The rod is rotated at constant angular speed about a perpendicular axis passing through its centre. The ratio of the magnitudes of the magnetic moment of the system and its angular momentum about the centre of the rod is

• 5)

A coil having n turns and resistance R is connected with a galvanometer of resistance 4R. This combination is moved in time t seconds from a magnetic flux ${ \phi }_{ 1 }$ Weber to ${ \phi }_{ 2 }$ Weber. The induced current in the circuit is :

#### 12th Standard CBSE Physics Public Model Question Paper I 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

Electric field intensity (E) due to an electric dipole varies with distance (r) of the point from the centre of dipole as:

• 2)

If $\oint _{ s }^{ }{ E.ds } =0$ over a surface, then

• 3)

An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude

• 4)

A particle of mass m and charge q is accelerated through a potential difference V to a velocity $\vec { \upsilon }$ towards south. The particle enters a region with both a magnetic field $\vec { B }$ (pointing eastwards) and electric field $\vec { E }$ (pointing downwards). The particle travels with a constant velocity through this region. The potential difference V through this region should be equal to

• 5)

SI unit of magnetic flux is

#### 12th CBSE Physics - Public Model Question Paper 2019 - 2020 - by Sharma - Kochi - View & Read

• 1)

Electric dipole moment is

• 2)

A condenser is charged to double its initial potential. The energy stored in the condenser becomes x times, where x=

• 3)

A long straight wire of radius a carries a steady current i. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at a/2 and 2 a is

• 4)

A galvanometer of resistance $25\Omega$ is connected to a battery of 2 volt along with a resistance in series. When the value of this resistance is $3000\Omega ,$ a full scale deflection of 30 units is obtained in the galvanometer. In order to reduce this deflection 10 20 units, the resistance in series will be

• 5)

Q factor of resonance is given by

#### CBSE 12th Physics - Ray Optics and Optical Instruments Model Question Paper - by Sharma - Kochi - View & Read

• 1)

A Concave mirror form the real image of an object which is magnified 4 times. The object is moved 3 cm away, the magnification of the image is 3 times. What is the focal length of the mirror?

• 2)

A 4 cm thick layer of water covers a 6 cm thick glass slab. Acoin placed at the bottom of the slab and is being observed from the air side along the normal to the surface. Find the apprent position of the coin from

• 3)

If in a plano-convex lens, radius of curvature of convex surface is 10 cm and the focal length of the lens is 30 cm. The refractive index of the material of the lens will be

• 4)

Two lamps of powers ${ P }_{ 1 }$and ${ P }_{ 2 }$ are placed on either side of apaper having an oil spot. The lamps are at 1m and 2 m respectively, On either side of the paper and the oil spot is invisible. What is the value of  ${ P }_{ 1 }/{ P }_{ 2 }$?

#### CBSE 12th Physics - Communication Systems Model Question Paper - by Sharma - Kochi - View & Read

• 1)

Frequencies in the UHF range normally propagate by means of:

• 2)

A speech signal of 3kHz is used to modulate a carrier signal of frequency 1MHz, using amplitude modulation.The frequencies of the sidebands will be

• 3)

Identify the mathematical expression for amplitude modulated wave:

• 4)

Audio sine waves of 3kHz frequency are used to amplitude modulate a carrier signal of 1.5 MHz. Which of the following statements are true?

• 5)

Out of the following, which is not an essential element of a communication system?

#### CBSE 12th Physics - Electronic Devices Model Question Paper - by Sharma - Kochi - View & Read

• 1)

In good conductorsof electricity the type of bonding that exists is

• 2)

In a p-type semiconductor, the acceptor level is situated 60m eV above the valence band. The maximum wavelength of light required to produce a hole will be [use hc = 12400eV ]

• 3)

In the middle of the depletion layer of a review biased p-n junction,the

• 4)

An n-p-n transistor having a.c. current gain of 50 to be used to make an amplifier of power gain of 300.What will be the voltage gain of the amplifier

• 5)

For transistor amplifier,the voltage gain

#### CBSE 12th Physics - Atoms and Nuclei Model Question Paper - by Sharma - Kochi - View & Read

• 1)

Taking the Bohr radius as a0=53pm, the radius of Li++ ion its ground state, on the basis of Boh''s model, will be about

• 2)

The Bohr model for the spectre of a H-atom

• 3)

Two H atoms in the ground state collide inelastically. The maximum amount by which their combined kinetic energy is reduced is

#### 12th Standard CBSE Physics - Dual Nature of Radiation and Matter Model Question Paper - by Sharma - Kochi - View & Read

• 1)

An electron (mass $m$) with an initial velocity $v={ v }_{ 0 }\vec { i } ({ v }_{ 0 }>0)\quad$ is an electric field $v={ v }_{ 0 }\vec { i } ({ v }_{ 0 }>0)\quad$ its de-Broglie wave-length at time $t$ is given by

• 2)

A and B are two metals with threshold frequencies $1.8\times { 10 }^{ 14 }Hz$and $2.2\times { 10 }^{ 14 }Hz$Two identical photons of energy 0.825 eV each are incident on them.Then photoelectrons are emitted in (take $h=6.63\times { 10 }^{ -34 }J/s$

• 3)

Silver has a work function of 4.7eV when ultraviolet light of wavelength 100 nm is incident upon it, a potential 0f 7.7 is required to stop the photoelectrons from reaching the collector plate.How much potential will be required to stop the photoelectrons when light of wavelength 200 nm is incident upon silver?

• 4)

The wavelength of a KeV photon is $1.24\times { 10 }^{ -9 }m$ .What is the frequency of 1 MeV photon?

• 5)

If v is frequency,$\lambda$is the wavelength and $\overline { v }$is the wave number then the energy of a photon can be represented by

#### CBSE 12th Physics - Wave Optics Model Question Paper - by Sharma - Kochi - View & Read

• 1)

In a young's double slit experiment, the source is white light. One of the holes is covered by a red filter and another by a blue filter. In this case

• 2)

Consider the diffraction pattern for a small pinhole. As the size of the hole is increased

• 3)

Which is not true for the image formed in a plane mirror? The image is

• 4)

Refractive index of glass w.r.t. water is 9/8. What is the speed of light in water? Given speed of light in glass is $2\times 10^{ 8 } \ m/s$ .

• 5)

An astronomical telescope has a magnifying power of 10. In normal adjustment, distance between the objective and eye piece is 22 cm. The focal length of objective lens is

#### CBSE 12th Physics - Electromagnetic Waves Model Question Paper - by Sharma - Kochi - View & Read

• 1)

A linearly polarized electromagnetic wave given as $E={ E }_{ 0 }\overset { \wedge }{ i } cos \ (kz-wt)$ incident wall at $z=a$ . Assuming that the material of the wall os optically inactive, the reflected wave will be given as

• 2)

An $EM$ wave radiates out waves from a dipole antenna, with $E_{ 0 }$ as the amplitude of its electric field vector. The electric field $E_{ 0 }$ which transports significant energy from the source falls off as:

• 3)

The source of electromagnetic waves can be a charge

• 4)

An EM wave of intensity I falls on a surface kept in vacuum and experts radiation pressure kept in vacuum and experts radiation pressure p on it. Which of the following are true?

• 5)

The velocity of light in vacuum can be changed by changing

#### CBSE 12th Physics - Electromagnetic Induction and Alternating Currents Model Question Paper - by Sharma - Kochi - View & Read

• 1)

In the relation $\phi$ = BA cos $\theta$, $\theta$ is angle........

• 2)

Out of the following, choose the correct relation

• 3)

Phase difference between voltage across L and C in series is

• 4)

The relation $\frac { { E }_{ s } }{ { E }_{ p } } =\frac { { n }_{ s } }{ { n }_{ p } }$ is applied only to

• 5)

An e.m.f. is produced in a coil, which is not connected to an external voltage source. This can be due to

#### CBSE 12th Physics - Magnetic Effects of Current Model Question Paper - by Sharma - Kochi - View & Read

• 1)

The magnetic field at a perpendicular distance of 2 cm from an infinite straight current carrying conductor is 2x10-6 T. The current in the wire is

• 2)

Ampere's circuital law can be derived from

• 3)

A circular coil carrying current behaves as a

• 4)

A circular current loop of magnetic moment M is in arbitrary orientation in an external magnetic field.$\overset { \rightarrow }{ B }$ The work does to rotate the loop by $30°$about an axis perpendicular to its plane is

• 5)

A toroid of n turns, mean radius R and cross-sectional radius carries a current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment $\overset { \rightarrow }{ M }$

#### CBSE 12th Physics - Current Electricity Model Question Paper - by Sharma - Kochi - View & Read

• 1)

A steady current is flowing in a cylindrical conductor. Is there any electric field within the conductor?

• 2)

How can you keep a constant current inside a conductor?

• 3)

What is the resistance of carbon resistor on which the colour of rings in sequence is black, brown, black and gold.

• 4)

A 10Ω thick wire is stretched so that its length becomes three times. Assuming that there is no change in its density on stretching. Calculate the resistance of new wire

• 5)

You are given 8 $\Omega$ resistor. What length of wire of resistance 120 Ωm-1 should be joined in parallel with it to get a value of 6 $\Omega$ ?

#### CBSE 12th Physics - Electrostatics Model Question Paper - by Sharma - Kochi - View & Read

• 1)

The SI unit of electric field intensity is

• 2)

Electric field intensity (E) due to an electric dipole varies with distance (r) of the point from the centre of dipole as:

• 3)

Electrostatic potential V at a point, distant r from a charge q varies as

• 4)

1 stat-Coulomb = ......... Coulomb

• 5)

If $\oint _{ s }^{ }{ E.ds } =0$ over a surface, then

#### CBSE 12th Physics - Full Syllabus One Mark Question Paper with Answer Key - by Sharma - Kochi - View & Read

• 1)

Electric dipole moment is

• 2)

Potential energy of an electric dipole held at an angle $\theta$ in a uniform electric field is zero when $\theta=$

• 3)

A closed surface in vacuum encloses charges -q and +3q. Another charge -2q lies outside the surface. Total electric flux over the surface is

• 4)

Which of the following is not an insulator?

• 5)

The cause of charging is actual transfer of protons

#### CBSE 12th Physics - Full Syllabus Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

How rubbing of the two bodies produces electricity?

• 2)

The electric field by E = ${1000\over r}Vm^{-1}$, and is directed outwards. What is the sign of the charge on the wire? If two points A and B are situated such that $r_A=0.2m$ and $r_B=0.4m$, find the value of $(V_B-V_A)$.

• 3)

Three charges (all q = 10 C) are placed at the edge of an equilateral triangle of side 2 m. Find the net potential energy of the system.

• 4)

A capacitor of 200 pF is charged by a 300 V battery. The battery is then disconnected and the charge capacitor is connected to another uncharged capacitor 0f 100 pF. Calculate the difference between the final energy stored in the combined system and the initial energy stored in the single capacitor.  The difference between the final energy stored in combined system and initial energy stored in single capacitor is equal to loss in energy  $(=\frac { { C }_{ 1 }{ C }_{ 2 }\left( { V }_{ 1 }-{ V }_{ 2 } \right) ^{ 2 } }{ 2\left( { C }_{ 1 }+{ C }_{ 2 } \right) } )$

• 5)

Using Gauss's theorem, deduce an expression for the electric field intensity at any point due to a thin, infinitely long wire of charge/length '$\lambda$' C\m

#### CBSE 12th Physics - Full Syllabus Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

A rectangular coil of n turns each of area A, carrying current I, when suspended in a uniform magnetic field B, experiences a torque
$\tau =nI \ BA \ sin\theta$
Where is $\theta$ the angle which a normal drawn on the plane of coil makes with the direction of magnetic field. This torque tends to rotate the coil and bring it in an equilibrium position. In the stable equilibrium state, the resultant force on the coil is zero. The torque on the coil is also zero and the coil has minimum potential energy.
(i) In which position, a current carrying coil suspended in uniform magnetic field experiences (a) minimum torque and (b) maximum torque?
(ii) a circular coil of 200 turns, radius 5 cm carries a current of 2.0 A. It is suspended vertically in a uniform horizontal magnetic field of 0.20 T, with the plane of the coil making an angle with $60°$ the field lines. Calculate the magnitude of the torque that must be applied on it to prevent it from turning.
(iii) what is the basic value displayed by the above study?

• 2)

Derive the expression for the energy stored in parallel plate capacitor. Hence, obtain the expression for the energy density of the electric field.
A fully charged parallel plate capacitor is connected across an uncharged identical capacitor.Show that the energy stored in the combination is less than stored initially in the single capacitor.

• 3)

In Akash's classroom the fan above the teacher was running very slowly. Due to which his teacher was sweating and was restless and tired. All his classmates wanted to rectify this. They called for an electrician who came and changed the capacitor only after which the fan started running fast.
(a) What values did Akash and his classmates have?
(b) What energy is stored in the capacitor and where?

• 4)

Two point charges $+4\mu C$ and $-6\mu C$ are separated by a distance of 20cm in air .At what point on the line joining the two charges is the electric potential zero?

#### CBSE 12th Physics - Full Syllabus Two Marks Questions - by Sharma - Kochi - View & Read

• 1)

Give four properties of electric charges.

• 2)

If the potential difference across a capacitor is doubled, what happens to :
(a) the charge on the capacitor and
(b) the energy stored in the capacitor

• 3)

Ordinary rubber is an insulator. But the special rubber tyres of aircraft's are made slightly conducting. Why is this necessary?

• 4)

An electric dipole is held in an uniform electric field. Using suitable diagram, show at it doesn't undergo any translatory motion, and (ii) derive an expression for torque acting on it and specify its direction.

• 5)

At 0oC, the resistance of a conductor B is n times that of conductor A.  The temperature coefficients of resistance of A and B are $\alpha_1$ and $\alpha_2$ respectively. For the series combination of the two conductors find (a) the resistance at 0oC (b) the temperature coefficient of resistance.

#### CBSE 12th Physics - Wave Optics Problems Questions - by Sharma - Kochi - View & Read

• 1)

The refractive index of water is 4/3. Obtain the value of the semivertical angle of the cone within which the entire outside view would be confined for a fish under water. Draw an appropriate ray diagram

• 2)

A lens forms a real image of an object. The distance of the object to the lens is 4 cm and the distance of the image from the lens is v cm. The given graph shows the variation of v with u. (i) What is the nature of the lens? (ii) Using this graph, find the focal length of this lens.

• 3)

A ray of light passes through an equilateral glass prism, such that the angle of incidence is equal to the angle of emergence. If the angle of emergence is ¾ times the angle of the prism, Calculate the refractive index of the glass prism

• 4)

(a) A point object is placed in front of a double convex lens (of refractive index n =n2/n1 with respect air) with its spherical faces of radii of curvature R1 and R2.. Show the path of rays due to surface to obtain the formation of the real image of the object.
Hence obtain the lens maker's formula for a thin lens.
(b) A double convex lens having both faces of the same radius of curvature has refractive index 1.55. Find out the radius of curvature of the lens required to get the focal length of 20 cm.

• 5)

Light of wavelength $5000\overset { \circ }{ A }$ falls on a plane reflecting surface. What are the wavelength and frequency of reflected light? For what angle of incidence is the reflected ray normal to the incident ray?

#### CBSE 12th Physics - Electromagnetic Waves Problems Questions - by Sharma - Kochi - View & Read

• 1)

A parallel plate capacitor has circular plates each of radius 6.0 cm. It is charged such that the electric field in the gap between its plates rises constantly at the rate of 1010 V cm-1 s-1. What is the displacement current?

• 2)

There is a parallel plate capacitor of capacitance $2.0\mu F.$ The voltage between the plates of parallel plate capacitor is changing at the rate of 6.0 V s-1 . What is the displacement current in the capacitor?

• 3)

How would you establish an instantaneous displacement current of 2.0 A in the space between the two parallel plates of $1\mu F$ capacitor?

• 4)

A plane electromagnetic wave of frequency 25MHz travels in free space along the x-direction. At a particular point in space and time the electric vector is $\overrightarrow { E } =6.3V/m\hat { j }$Calculate $\overrightarrow { B }$ at this point.

• 5)

Calculate the peak values of electric and magnetic fields produced by the radiation coming from a 100 watt bulb at a distance of 3 m. Assume that the efficiency of the bulb is 2.5% and it is a point source?

#### CBSE 12th Physics - Electromagnetic Induction and Alternating Currents Problems Questions - by Sharma - Kochi - View & Read

• 1)

A mahnetic field of flux density 10 T acts normal to a coil of 50 turns having 50cm2 area. Find emf induced if the coil is removed from the magnetic field in 0.1sec.

• 2)

The magnetic flux through a coil is varying according to the relation $\phi$=(5t3+4t2+2t-5). Calculate the induced current through the coil at t=2s, if resistance of coil is 5 ohm.

• 3)

Find the change in current in an inductor of 10 H in which the e.m.f. induced is 300 V in 10-2 sec. Also, find the change in magnetic flux.

• 4)

The self inductance of a coil having 200 turns is 10mH. Compute the total flux linked with the coil. Also, determine the magnetic flux through the cross section of the coil, corresponging to curent of 4mA.

• 5)

Two coils have mutual inductance of 1.5 henry. If current in primary circuit is raised to 5 ampere in one millisecond after closing the circuit, what is the e.m.f. induced in  the secondary?

#### CBSE 12th Physics - Magnetic Effects of Current Problems Questions - by Sharma - Kochi - View & Read

• 1)

A current element 3 dl is at (0,0,0) along y-axis. if dl =1 cm, find the magnetic field at a distance 20 cm on the x-axis.

• 2)

A wire of radius 0.8 cm carries a current of 100 A which is uniformly distributed over its cross-section. Find the magnetic field (a) at 0.2 cm from the axis of the wire (b) at the surface of the wire and (c) at a point outside the wire 0.4 cm from the surface of the wire. Neglect the permeability of the material of wire.

• 3)

A solenoid of length 0.5 m has a radius of 1 cm and is made up of 500 turns. It carries a current of 5 A. What is the magnitude of the magnetic field inside the solenoid ?

• 4)

A proton enters a magnetic field of flux density 2.5 T with a speed of 1.5 x 107 ms-1 at an angle of 30o with the field. Find the force on the proton.

#### CBSE 12th Physics - Current Electricity Problems Questions - by Sharma - Kochi - View & Read

• 1)

In the arrangement of resistors shown here, what fraction of I will pass through 5$\Omega$ resistor?

• 2)

You are given a 8 $\Omega$ resistor. What length of constant wire of resistance 120$\Omega$ m-1 should be joined in parallel with it to get a value of 6$\Omega$?

• 3)

Two identical cells of e.m.f 1.5V each joined in parallel provide supply to an external circuit consisting of two resistors of 17$\Omega$ each joined in parallel. A very high resistance voltmeter reads the terminal voltage of the cells to be 1.4V. What is the internal resistance of each cell?

• 4)

Storage battery of a car has an e.m.f of 12V. If the internal resistance of the battery is 0.4$\Omega$ What is the maximum current that can be drawn from the battery?

• 5)

Four identical cells, each of emf 2V are joined in parallel providing supply of current to external circuit consisting of two 15$\Omega$ resistors joined in parallel. The terminal voltage of the cells as read by an ideal voltmeter is 1.6V Calculate the internal resistance of each cell.

#### CBSE 12th Physics - Electrostatics Problems Questions - by Sharma - Kochi - View & Read

• 1)

A charged Particle q is shot towards another charged particle Q which is fixed , with a speed v. It approaches Q up to a closet distance r and then returns, If q were given a speed 2 v the n find the closet distance of approach.

• 2)

Two Capacitors of capacitace 6$\mu$F and 12$\mu$F ae connnected in series with tha battery the volatage across the 6$\mu$F capacitor is 2 volt, Compute the total battery voltage.

• 3)

There is a sphere of radius 20cm.What charge should be given to the sphere so that it acquires a surface charge density of ${ 3 }/{ \pi }{ cm }^{ -2 }$?

• 4)

A regular hexagon of side 10 cm has a charge 5$\mu$ C at each of its vertices.calculate the potential at the hexagon.

#### 12th CBSE Physics - Ray Optics and Optical Instruments Five Marks Model Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

Suppose while sitting in a parked car, you notice a jogger approaching towards you in the side view mirror of R = 2 m. If the jogger is running at a speed of 5 m s-1, how fast the image of the jogger appear to move when the jogger is
(a) 39 m,
(b) 29 m,
(c) 19 m, and
(d) 9 m away

• 2)

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

• 3)

A small bulb is placed at the bottom of a tank containing water to a depth of 80cm. What is the area of the surface of water through which light from the bulb can emerge out? Refractive index of water is 1.33. (Consider the bulb to be a point source.)

• 4)

Double-convex lenses are to be manufactured from a glass orefractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20 cm?

• 5)

An object of size 3.0 cm is placed 14 cm in front of a concave lens of focal length 21cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?

#### CBSE 12th Standard Physics - Communication Systems Five Mark Model Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

Mohan went to the market to purchase a TV set. He got confused with so many features and functions of electronic appliances. He took the help of his friend Sohan, a science student.Sohan explained him about the communication system, digital and analog signals. This knowledge proved of great help to Mohan in purchasing a colour TV.
(i)  What do you mean by the term communication?
(ii) Which type of signals are better?
(iii) What type of nature Sohan has?
(iv)What is the minimum number of communication satellites required for global communication coverage?

• 2)

In the famous conversation, Rakesh Sharma, the first Indian Astronaut in space, was asked by the Prime Minister Indira Gandhi as to how India looked from space.To which he replied,'Sare Jahan Se Achcha' (better than the whole world).
(i)   Which scientific mode of communication enabled the Prime Minister to speak to the Astronaut?
(ii)   Name the scientific values displayed in this anecdote.
(iii) Which values are being reflected in the reply given by the astronaut?
(iv) Give one more example of this scientific mode of communication in everyday life situations.

• 3)

Arnab was talking on his mobile to his friend for a long time. After his conversation was over, his sister Anita advised him that if his conversation was of such a long duration, it would be better to talk through a land line.
(a) Why is it considered harmful to use a mobile phone for a long duration?
(b) Which values are reflected in the advice of his sister Anita?
(c) A message signal of frequency 10 kHz is superposed to modulate a carrier wave of frequency 1 MHz. Determine the sidebands produced.

• 4)

Sweta had no proper knowledge about point-to-point communication and broadcast. So, she took help from her friend Rakhi explained him that in point-to-point communication mode, the communication takes place over a link between a single transmitter and a receiver. The example of this mode of communication is telephony. But in broadcast mode, there are a number of receivers corresponding to a single transmitter. The examples of this mode of communication are radio and television. Then Sweta was convinced with answer of Rakhi,
(a) What are the values displayed by Rakhi?b
(b) A message signal of frequency 10 kHz and peak voltage of 10 V is used to modulate a frequency of 1 MHz and peak voltage of 20 V. Determine
(i) modulation index
(ii) frequency of the side band produced.

• 5)

When Sunita, a class XII student, came to know that her parents are planning to rent out the top floor of their house to a mobile company she protested. She tried hard to convince her parents that this move would be a health hazard.
Ultimately her parents agreed :
(i)  In what way can the setting up of transmission tower by a mobile company in a residential colony prove to be injurious to health?
(ii)  By objecting to this move of her parents, what value did Sunita display?
(iii)  Estimate the range of e.m. waves which can be transmitted by an antenna of height 20m. (Given radius of the earth = 6400 km)

#### 12th Standard CBSE Physics - Electronic Devices Five Mark Model Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

Suppose a 'n'-type wafer is created by doping Si crystal having  $5\times10^{ 28 }$atoms/${ m }^{ 3 }$with 1 ppm concentration of As.On the surface 200 ppm Boron is added to create $'p'$region in this wafer. Considering ${ n }_{ i }=1.5\times10^{ 16 }m^{ -3 }$ (i) Calculate the densities of the charge carriers in the   $n\& p$ regions.(ii)Comment which carriers would contribute largely for the reverse saturation current when diode is reverse biased.

• 2)

Zener diode is a specially designed $p-n$ junction diode,in which both $p-side$ and $n-side$ of $p-n$junction are heavily doped.The zener diode is designed to operate in the reverse break down voltage region continuously without being damaged ? Zener diode is used to remove the fluctuations  from the given voltage and thereby provides a voltage of constant magnitude (i.e., zener diode is used as voltage regulator).
(i) What is the most important use of Zener diode?
(ii)What are the essential conditions for proper working of Zener diode?
(iii)What do you learn from the above study?

• 3)

Manoj wanted to do social work during vacations.He visited a remote village where there was no electricity.He made up his mind to help the villagers for getting the solar panels.For this he educated the villagers about techonology and uses of solar panels.he requested the villagers to Villagers agreed and applied for the solar panels.They got the same from government at reduced price.When the solar panels started working,the villagers were happy.
(i)What is solar panel?
(ii) What is the basic principle of working of a solar cell?
(iii) What are the basic values you assess in Manoj?

• 4)

Meeta father was driving her to the school.At the traffic signal she noticed that each traffic light was  made of many lights instead of a single bulb.When Meeta asked this question to her father's he explained the reason for this.
Answer the following questions based on above information:
(i) What were the values displayed by Meeta and her father?
(ii) What are the tiny lights in traffic signals called and how do these operate?

• 5)

(i) Differentiate between three segments of a transistor on the basis of their size and level of doping
(ii) How is a transistor biased to be in active state?
(iii) With the help of necessary circuit diagram, describe briefly how n-p-n transistor in CE configuration amplifies a small sinusoidal input voltage. Write the expression for the AC current gain.

#### CBSE 12th Physics - Electromagnetic Waves Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

How would you set up an instantaneous displacement current of 2.0 A within the space between the two parallel plates of $3_{ \mu }F$ capacitance?

• 2)

A parallel plate capacitor is made out of two rectangular metal plates of sides 30 cm $\times$15 cm and separated by a distance of 2.0 mm. The capacitor is charged in such a way that the charging current has a constant value of 100 mA. What must be the rate of change of potential of the charging source to ensure this and what will be the displacement current in the region between the capacitor plates?

• 3)

Nitin and Rajeev were studying the effect of certain radiations on flower plants. Nitin exposed his plants to ultraviolet rays, found that his plants got damaged after few days.Rajeev exposed his plants to infrared rays, found that his plants had a beautiful bloom, after a few days.
(i) What is the difference between ultraviolet rays and infrared rays
(ii) Why were the plants exposed to ultraviolet rays damaged and the plants exposed infrared rays had a beautiful bloom?
(iii) What are the basic values you have learnt from this study

• 4)

Draw a labelled diagram of Hertz's experiment. Explain how electromagnetic radiations are produced using this set-up.

• 5)

Akil was playing cricket with his friends, when a ball hit friend Bharat on his leg. Bharat screamed with pain. Akhil rushed towards him and comforted him and asked him not to move his leg. He quickly took out his cell phone and called up Bharat's parents and briefed them about the incident. In 10 minutes Bharat was taken to the nearby hospital and was examined by the doctor who advised for an X-rays test which confirmed a hairline fracture.
(a) How are X-rays produced?
(b) Mention one another application of X-rays.
(c) Mention two qualities of Akhil which are reflected from above situation.

#### CBSE 12th Physics - Dual Nature of Radiation and Matter Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

Radiation has dual nature,i.e., it possesses the properties of both; wave and particle.This prompted de-Broglie to predict dual nature of moving material particles.Thus waves are associated with moving material particles which are called matter waves. The wavelength of matter wave is given by $\lambda =\frac { h }{ mv }$, where m is the mass, v is the speed of the particle and h is Plank's constant. Read the above paragraph and answer the following questions;
(i) How was the wave nature of the electron established?
(ii) What are the de-Broglie wavelength associated with a particle (i) at rest (ii) moving with infinite speed?
(iii) What are the basic values displayed with this study?

• 2)

Mohan thought that there are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. But, can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength? He got confused and could not find its answer. Then he requested his friend Sohan. Sohan explained him that in the first case, energy given out is less than the energy supplied. But in the second case, the material has to supply the energy as the emitted photon has to supply the energy as the emitted photon has more energy, which cannot happen for stable substances.
(a) What values do you notice in Sohan?
(b) Consider a metal exposed to light of wavelength 600 nm. The maximum energy of the electron doubles when light of wavelength 400 nm is used. Find the work function in eV.

• 3)

Ram knows that red light has greater and so it is much bright, but in case of photoelectric emission it cannot produce the emission of electrons from a clean zinc surface, while even weak ultraviolet radiation can do so. He could not know specific cause of such thing. Then he went to his friend Shyam for its specific explanation. Shyam explained him that the photoemission of electron does not depend on the intensity while it depends on the frequency and thus on the energy of photon of incident light. The energy of photon of red light cannot emit photoelectrons. Similarly, the energy of photon of ultraviolet light is greater than the work function of zinc, so ultraviolet light can emit photoelectrons.
(a) What values are noticed in Shyam?
(b) The work functions of lithium and copper are 2.3eV and 4eV respectively. Which of these metals are useful for the photoelectric cell working with visible light? Explain.

• 4)

A function was organised in the school auditorum. There was 500 sitting arrangement in the auditorium. When entry started, students entered in groups and so counting became a great problem. Then principle of the school ordered science students managed the situation and now all the students used to enter the hall one by one. This helped them to maintain discipline and counting became easy with the help of a scientific device used by these students.
Name the scientific device which is based on application of photoelectric effect.

#### CBSE 12th Physics - Ray Optics and Optical Instruments Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

• 2)

A tank is filled with water to a height of 12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be 9.4 cm. What is the refractive index of water? If water is replaced by a liquid of refractive index 1.63 up to the same height, by what distance would the microscope have to be moved to focus on the needle again?

• 3)

A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is
(a) a convex lens of focal length 20 cm, and
(b) a concave lens of focal length 16 cm?

• 4)

An object of size 3.0 cm is placed 14 cm in front of a concave lens of focal length 21cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?

• 5)

Use the mirror equation to deduce that:
(a) an object placed between f and 2f of a concave mirror produces a real image beyond 2f.
(b) a convex mirror always produces a virtual image independent of the location of the object.
(c) the virtual image produced by a convex mirror is always diminished in size and is located between the focus and the pole.
(d) an object placed between the pole and focus of a concave mirror produces a virtual and enlarged image.
[Note: This exercise helps you deduce algebraically properties of images that one obtains from explicit ray diagrams.]

#### CBSE 12th Physics - Electronic Devices Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

Zener diode is a specially designed $p-n$ junction diode,in which both $p-side$ and $n-side$ of $p-n$junction are heavily doped.The zener diode is designed to operate in the reverse break down voltage region continuously without being damaged ? Zener diode is used to remove the fluctuations  from the given voltage and thereby provides a voltage of constant magnitude (i.e., zener diode is used as voltage regulator).
(i) What is the most important use of Zener diode?
(ii)What are the essential conditions for proper working of Zener diode?
(iii)What do you learn from the above study?

• 2)

Kritika Singh was enjoying TV programme at her home with her younger brother Surya at night. Suddenly, the light went off causing darkness all over. Surya asked her to bring candle along with matchstick to put the TV switch OFF. Kritika at once picked the mobile phone and pressed the button lighting up the surrounding. Her younger brother was surprised and asked, where the light was coming. Kritika proudly showed her mobile.
(i) Which value is displayed by Kritika?
(ii) Name the material used in the formation of LED.
(iii) LED works, in which biasing?

• 3)

Shorya usually enjoyed loud music. One day his music system was not producing very loud sound. Shorya gets disappointed. He discussed his problem with his big brother Kamal. Kamal advised him to connect an amplifier in series with the amplifier of the stereo system. This increased the sound of Shroya's music system considerably. Read the above passage and answer the following questions:
(i) Which value is displayed by Kamal?
(ii) Why the loudness of music system get increased on connecting amplifier?
(iii) Give the equation for current gain in the transistor as an amplifier.

• 4)

Sanjay was preparing an electronic project for science exhibition. He required to light the LED using a 6 V supply. LEDs need only a very small current to make them light and they do not heat up in use. So he put a resistor in series to limit the current. Then there would be p.d. of 4 V across the resistor as there is always 2.0 V across the LED itself when it is conducting. The current should be 10 mA through both LED and the resistor. He could use the resistance by equation, R = V/I to calculate the value of R.
$R=\frac { V }{ I } =\frac { 4V }{ 10mA } =\frac { 4V }{ 0.01A } =400V$
Thus the protecting resistor should be around 400 $\Omega$
(a) What are the values exhibited by Sanjay?
(b) A semiconductor has equal electron and hole concentration of $6\times 10^{ 8 }/m^{ 3 }$ . On doping with certain impurity, electron concentration increases to $9\times 10^{ 12 }/m^{ 3 }$ .
(i) Identify the new semiconductor obtained after doping.
(ii) Calculate the new hole concentration.
(iii) How does the energy gap vary with doping?

• 5)

Anita was thinking that C, Si and Ge have same lattice structure, but C is insulator while Si and Ge are intrinsic semiconductors. For its answer she met her friend Sunita. Sunita explained her that the four bonding electrons of C, Si and Ge lie respectively in the second, third and fourth orbit. So, energy required to take out an electron from these atoms known as ionisation energy Ig will be the least for Ge, followed by Si and the highest for the least for Ge, followed by Si and the highest for C. Hence number of free electrons for conduction in Ge and Si are significant while negligibly small for C.
(a) What are the values shown by Sunita ?
(b) If a pure silicon crystal has $5\times { 10 }^{ 28 }atoms/{ m }^{ 3 }$. It is doped by 1ppm concentration of pentavalent arsenic.
If n1 = 1.5 x 1016/m3, then calculate the number of electrons and holes.

#### 12th Standard CBSE Physics - Wave Optics Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

The magnifying power of an astronomical telescope in the normal adjustment position is 100.The distance between the objective and eye piece is 101cm.Calculate the focal lengths of objective and eye piece.

• 2)

An astronomical telescope is designed to have a magnifying power of 50 in normal adjustment.If the length pf the tube is 120cm, find the powers of objective and eye piece.

• 3)

Kanchan while driving her scooty sees a woman behind driving a moped through his rear view mirror. She sees that her saree is almost touching the wheels of the vehicle. She stops her and alert that it may cause a severe accident.
(i) What values do you observe in Kanchan?
(ii) Name the mirror used in rear view in scooty. Draw a ray diagram for the same.

• 4)

(i) You have learnt that plane and convex mirrors produce virtual images of objects. Can they produce real images under some circumstances? Expalin.
(ii) A virtual image, we always say, cannot be caught on a screen. Yet when we see a virtual image, we are obviously bringing it on to the screen (i.e. the retina) of our eye. Is there a contradiction?
(iii) A diver under water, looks obliquely at a fisherman standing on the bank of a lake. Would the fisherman look taller or shorter to the diver than what he actually is?
(iv) Does the apparent depth of a tank of water change, if viewed obliquely? If so, does the apparent depth increase or decrease?

• 5)

(i) In a double slit experiment using light of wavelength 600 nm, the angular width of the fringe formed on a distant screen is $0.1^o$ . Find the spacing between the two slits.
(ii) Light of wavelength 5000$\dot { A }$ propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected?

#### 12th Standard CBSE Physics - Communication Systems Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

Mohan went to the market to purchase a TV set. He got confused with so many features and functions of electronic appliances. He took the help of his friend Sohan, a science student.Sohan explained him about the communication system, digital and analog signals. This knowledge proved of great help to Mohan in purchasing a colour TV.
(i)  What do you mean by the term communication?
(ii) Which type of signals are better?
(iii) What type of nature Sohan has?
(iv)What is the minimum number of communication satellites required for global communication coverage?

• 2)

Raj was cycling from his village to a neighbouring village.On the way, he met an old man who was walking in the direction of the same neighbouring village. Raj invited the old man to sit on his cycle and took him to the neighbouring village.The old man got down from the cycle, thanked Raj and gave him blessing.
(i)  What are the values displayed by Raj?
(ii) Can you relate the given paragraph with the process of modulation?

• 3)

Anuj's mother was having constant headaches. After a medical check-up, she was diagnosed with tumour. Anuj realized there was a telecommunication tower very close to their house. He enquired from the doctor if the radiation from the tower could have caused the tumour. As the doctor supported his anxiety, he lodged a complaint with the police and ultimately succeeded in getting the tower removed to a distant place away the from residential colony?
(i)  What values were displayed by Anuj?
(ii) Anuj made a rough estimate about the height of the antenna to be 20 m from the ground. Calculate the maximum distance upto which radiations from the tower are likely to reach. Use the value of radius of the Earth = 6400 x 103 m.

• 4)

Sweta had no proper knowledge about point-to-point communication and broadcast. So, she took help from her friend Rakhi explained him that in point-to-point communication mode, the communication takes place over a link between a single transmitter and a receiver. The example of this mode of communication is telephony. But in broadcast mode, there are a number of receivers corresponding to a single transmitter. The examples of this mode of communication are radio and television. Then Sweta was convinced with answer of Rakhi,
(a) What are the values displayed by Rakhi?b
(b) A message signal of frequency 10 kHz and peak voltage of 10 V is used to modulate a frequency of 1 MHz and peak voltage of 20 V. Determine
(i) modulation index
(ii) frequency of the side band produced.

#### 12th Standard CBSE Physics - Atoms and Nuclei Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

A nuclear reactor is a powerful device, wherein nuclear energy is utilised for peaceful purposes. It is based upon controlled nuclear chain reaction. The nuclear chain reaction is controlled by the use of control rods (of boron or cadmium) and moderators like heavy water, graphite, etc. The whole reactor is protected with concrete walls 2 to 2.5 metre thick, so that radiations emitted during nuclear reactions may not produce harmful effects.
(i) Give any two merits of nuclear reactors.
(iii) Why do people often oppose the location site of a nuclear reactor? What do you suggest?

• 2)

According to Bohr's theory of hydrogen atom, total energy of electron in a stationary orbit is $E=-\frac { 13.6 }{ { n }^{ 2 } } eV,$ where n is the number of orbit. Clearly, total energy of electron in a stationary orbit is negative, which means the electron is bound to the nucleus and is not free to leave it. An n increases, value of negative energy decreases, i.e., energy is progressively larger in the outer orbits.
(i) What is total energy of electron in ground state of hydrogen atom? What does it imply?
(ii) Energy required to remove an electron is smaller when atoms is in any one excited state. Comment.
(iii) How is this concept translated in day to day life?

• 3)

On the basis of Bohr's theory of H-atom, total energy of electron in a stationary orbit is given by the relation
Where, n is the number of orbits. It is clear that total energy of electron in a stationary orbit is negative which implies that electron is bound to the nucleus and is not free to leave it. The value of negative energy decreases as n increases.
(i) What is the total energy of electron in ground state of hydrogen atom? What does it indicate?
(ii) Why does energy required to remove an electron is smaller when atom is in any one excited state?

• 4)

Asha's mother read an article in the newspaper about a disaster that took place at Chernobyl. She could not understand much from the article and asked a few questions from Asha regarding the article.
Asha tried to answer her mother's questions based on what she learnt in Class XII Physics?

#### 12th Standard CBSE Physics - Electromagnetic Induction and Alternating Currents Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

Distinguish between reactance and impedance. When a series combination of a coil of inductance L and a resistor of resistance R is connected across a 12 V, 50 Hz supply, a current of 0.5 A flows through the circuit. The current differs in phase from applied voltage by $\frac { \pi }{ 3 }$ radian. Calculate the value of L and R.

• 2)

A magnetic field $\overrightarrow { B } ={ B }_{ 0 }\sin { \left( \omega t \right) } \hat { k }$  covers a large region where a wire AB slides smoothly over two parallel conductors separated by a distance d. The wires are in the x-y plane. The wire AB (of length d) has resistance R and the parallel wires have negligible resistance. If AB is moving with velocity v. what is the current in the circuit. What is the force needed to keep the wire moving at constant velocity?

• 3)

What are conservative and non-conservative fields?

• 4)

What do you mean by quality factor or Q value of resonance circuit?

#### 12th Standard CBSE Physics - Atoms and Nuclei Five Mark Model Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

In the Auger process an atom makes a transition to a lower state without emitting a photon.the excess energy is transferred to an outer electron which may be ejected by the atom.(This is called an Auger electron).Assuming the nucleus to be massive, calculate the kinetic energy of an n=4 Auger electron emitted by Chromium by absorbing the energy from a n=2 to n=1 transition.

• 2)

A nuclear reactor is a powerful device, wherein nuclear energy is utilised for peaceful purposes. It is based upon controlled nuclear chain reaction. The nuclear chain reaction is controlled by the use of control rods (of boron or cadmium) and moderators like heavy water, graphite, etc. The whole reactor is protected with concrete walls 2 to 2.5 metre thick, so that radiations emitted during nuclear reactions may not produce harmful effects.
(i) Give any two merits of nuclear reactors.
(iii) Why do people often oppose the location site of a nuclear reactor? What do you suggest?

• 3)

Natural radioactivity is a spontaneous and self disruptive activity exhibited by a number of heavy elements in nature. Thus a heavy element disintegrates by itself without being forced by any external agent to do so.
According to radioactive decay law, the number of atoms disintegrated per second (i.e., rate of disintegration of radioactive atoms) at any instant is directly proportional to the number of radioactive atoms actually present in the sample at that instant, i.e., $-\frac { dN }{ dt } \propto N \ or \ R=-\frac { dN }{ dt } =\lambda N,$ where is $\lambda$ decay constant.
(i) The count rate from a radioactive sample containing ${ 10 }^{ 16 }$  atoms is $4\times { 10 }^{ 16 }$  per second. What is the value of decay constant?
(ii) Name the three types of radiactive radiations. Which one of them is most penetrating?
(iii) What does radioactive decay law imply in day to day life?

• 4)

Marie Curie and her teacher turned husband Pierre Curie worked hard to extract radium chloride (RaCl2) from uranium ore. They succeeded in 192 after a long struggle. About 0.19 g of RaCl2 was extracted and its radioactivity was studied. They were awarded by the noble prize, which they shared it which they shared it which they shared it with Henri Becquerel.
(i) What are the values shown by Marie Curie and her husband?
(ii) What do you understand by radioactivity? How the half-life period is related to the disintegration constant?
(iii)How is average-life of radioactive element related to half-life?

• 5)

On the basis of Bohr's theory of H-atom, total energy of electron in a stationary orbit is given by the relation
Where, n is the number of orbits. It is clear that total energy of electron in a stationary orbit is negative which implies that electron is bound to the nucleus and is not free to leave it. The value of negative energy decreases as n increases.
(i) What is the total energy of electron in ground state of hydrogen atom? What does it indicate?
(ii) Why does energy required to remove an electron is smaller when atom is in any one excited state?

#### 12th Standard CBSE Physics - Dual Nature of Radiation and Matter Five Mark Model Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

Consider a thin target $({ 10 }^{ -2 }$m square, ${ 10 }^{ -3 }$m thickness) of sodium, which produces a photocurrent of $100\mu A$ when a light of intensity 100w/${ m }^{ 2 }$ ( $(\lambda =660nm)$ falls on it.Find the probability that a photoelectron is produced when a photon strikes a sodium atom.[Take density of Na=0.97 kg/${ m }^{ 3 }$

• 2)

Radiation has dual nature,i.e., it possesses the properties of both; wave and particle.This prompted de-Broglie to predict dual nature of moving material particles.Thus waves are associated with moving material particles which are called matter waves. The wavelength of matter wave is given by $\lambda =\frac { h }{ mv }$, where m is the mass, v is the speed of the particle and h is Plank's constant. Read the above paragraph and answer the following questions;
(i) How was the wave nature of the electron established?
(ii) What are the de-Broglie wavelength associated with a particle (i) at rest (ii) moving with infinite speed?
(iii) What are the basic values displayed with this study?

• 3)

"Know your face beauty through comp[lexion meter" was one of the stall on science exhibition.A student interested to know his/her face beauty was made to stand on a platform and light from a lamp was made to fall on his/her face.The reading of complexion meter indicated the face beauty of the student which might be very fair, fair,semi-fair, semidark dark etc.
(i)What is the basic concept used in the working of complexion meter?
(ii) How is the face beauty recorded by face complexation meter?
(iii) What basic values do you learn from the above study?

• 4)

Neha's brother was riding the bike on the highway and she was sitting behind him. While sitting, at a place traffic signal turned red from green and her brother continued riding without noticing the signal change. Neha observed the whole situation and asked her brother to stop. Her brother felt happy on his sister's intelligence.
(i) Why Neha's brother became happy? What kind of value is expressed by Neha?
(ii) What are the principles that are used in maintaining traffic signals?
(iii) What is the leading physical quantity i8n the process? Write an equation for the speed of the photoelectron.

• 5)

Mohan thought that there are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. But, can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength? He got confused and could not find its answer. Then he requested his friend Sohan. Sohan explained him that in the first case, energy given out is less than the energy supplied. But in the second case, the material has to supply the energy as the emitted photon has to supply the energy as the emitted photon has more energy, which cannot happen for stable substances.
(a) What values do you notice in Sohan?
(b) Consider a metal exposed to light of wavelength 600 nm. The maximum energy of the electron doubles when light of wavelength 400 nm is used. Find the work function in eV.

#### 12th Standard CBSE Physics - Magnetic Effects of Current Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

Discuss relative strengths of electrical and magnetic forces.

• 2)

Discuss the sensitivity of a moving coil galvanometer.

• 3)

Find the expression for maximum energy of a charged particle accelerated by a cyclotron.

• 4)

Explain using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of
(ii) soft iron core?
Also, define the terms
(iii) current sensitivity and
(iv) voltage sensitivity of a galvanometer.
Why does increasing the current sensitivity not necessarily increase voltage sensitivity?

• 5)

(i) Derive an expression for torque acting on a bar magnet held at an angle $\theta$ with the direction of magnetic field.
(ii) A bar magnet of magnetic moment 5A-${ m }^{ 2 }$ has poles 0.20m apart. Calculate the pole strength.

#### 12th Standard CBSE Physics Current Electricity Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

(a) State Ohm's law.
(b) Define resistance. Give its SI unit.

• 2)

How will you establish the electrons carry current?

• 3)

Establish the relation between current and drift velocity.

• 4)

Define the term resistivity and write its S.I. unit. Derive the expression for the resistivity in terms of number density of free electrons and relaxation time.

• 5)

Ramaniamma was a childless window. She ran her life only by the pension for the Sr. citizens from the Government. When she switches ON one bulb in her house, all the other appliances get switched OFF. She could not even spend for an electrician. Sujatha living nearby decided to do something for her. She referred to Physics books and learned that the series combination for the household connection could be the reason. She called an electrician and had the circuit changed to parallel combination. The problem was solved and Ramaniamma was happy. She thanked Sujatha for her help to solve the problem.
(i) What are the values possessed by Sujatha?
(ii) Why a parallel combination is used for household? Give two advantages.

#### CBSE 12th Physics - Electrostatics Five Marks Questions - by Sharma - Kochi - View & Read

• 1)

A rectangular coil of n turns each of area A, carrying current I, when suspended in a uniform magnetic field B, experiences a torque
$\tau =nI \ BA \ sin\theta$
Where is $\theta$ the angle which a normal drawn on the plane of coil makes with the direction of magnetic field. This torque tends to rotate the coil and bring it in an equilibrium position. In the stable equilibrium state, the resultant force on the coil is zero. The torque on the coil is also zero and the coil has minimum potential energy.
(i) In which position, a current carrying coil suspended in uniform magnetic field experiences (a) minimum torque and (b) maximum torque?
(ii) a circular coil of 200 turns, radius 5 cm carries a current of 2.0 A. It is suspended vertically in a uniform horizontal magnetic field of 0.20 T, with the plane of the coil making an angle with $60°$ the field lines. Calculate the magnitude of the torque that must be applied on it to prevent it from turning.
(iii) what is the basic value displayed by the above study?

• 2)

A physics teacher tells his students in the class that in paramagnetic materials, every atom has some permanent magnetic dipole moment. In the absence of an external magnetic field, the atomic dipoles are randomly oriented so that average magnetic moment per unit volume of the material behaves as a magnet. When an external magnetic field is applied, the torque developed tries to align the atomic magnetic dipoles in the direction of the field. That is why the specimen gets magnetized weekly in the direction of the field.
(i) Name any three paramagnetic materials
(ii) Name any two ferromagnetic materials. How is their behavior different from that of paramagnetic materials?
(iii) The teacher asks the students how true is the famous saying: 'Spare the rod and spoil the child', comment.

• 3)

Use Gauss's theorem to find the electric field due to a uniformly charged infinitely large plane thin sheet with surface charge density $\sigma$ .
(ii) An infinitely large thin plane sheet has a uniform surface charge density $+\sigma$. Obtain the expression for the amount of work done in bringing a point charge q from infinity to a point, distant r, in front of the charged plane sheet.

• 4)

An electric dipole of dipole moment p consists of point charges +q and q separated by a distance 2a apart. , Deduce the expression for the electric field E due to the dipole at a distance x from the centre of the dipole on its axial line in terms of the dipole moment p. Hence, show that in the limit
x>> a, E $\longrightarrow$ 2P$(4\pi{\epsilon}_{0}{x}^{3})$.
Given the electric field in the region E = 2x $\hat{i}$, find the net electric flux through the cube and the charge enclosed by it.

• 5)

(i) If two similar large plates, each of area A having surface charge densities +σ and -σ are separated by a distance.d in air, find the expression for
(a) field at points between the 'two plates and on outer 'side of the plates. Specify the direction of the field in each case.
(b) the potential difference between the plates.
(c) the capacitance of the capacitor so formed.
(ii) Two metallic spheres of radii R and 2R are charged, so that both of these have same surface charge density σ.  If they are connected to each other with a conducting wire, in which direction will the charge flow and why?

#### 12th CBSE Physics - Electromagnetic Waves Five Mark Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

Sea water at frequency $v=4\times { 10 }^{ 8 }$Hz has permittivity $\varepsilon \ \approx \ 80 \ { \varepsilon }_{ 0 }$,  permeability $\mu ={ \mu }_{ 0 }$ and resistivity $\rho =0.25 \ \Omega -m$ Imagine a parallel plate capacitor immersed in sea water and driven by an alternating voltage source  $v(t) \ = \ { V }_{ 0 } \ sin \ (2\pi vt)$ . What fraction of the conduction current density is the displacement current density?

• 2)

Discuss the quantitative production of electromagnetic waves when a charge is accelerated.

• 3)

What are the uses of electromagnetic waves?

• 4)

A parallel plate capacitor made of circular plates each of radius R=5.0 cm has a capacitance C=96 pF. The capacitor is connected to a 220 V a.c supply with (argular) frequency of 300 rad ${ s }^{ -1 }$ .

• 5)

A radio can be tuned to any station in the 6 MHz to MHz band. What is the corresponding wavelength between 6 MHz and 9 MHz?

#### 12th CBSE Physics - Wave Optics Five Mark Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

Explain the terms interference of light and define constructive and destructive interference. Is law of conservation of energy obeyed?

• 2)

Distinguish between interference and diffraction.

• 3)

The mixture a pure liquid and a solution in a long vertical column (i.e., horizontal dimensions << vertical dimensions) produces diffusion of solute particles and hence a refractive index gradient along the vertical dimension. A ray of light entering the column at right angles to the vertical deviates from its original path. find the deviation in travelling a horizontal distance d<

• 4)

(i) Consider a thin lens placed between a source (S) and an observer (O). Let the thickness of the lens vary as $\omega (b)={ \omega }_{ 0 }-\frac { { b }^{ 2 } }{ a } ,$ where b is the vertical distance from the pole. ${ \omega }_{ 0 }$ is a constant. using Fermat's principle i.e., the time of transit for a ray between the source and observer is an extremum, find the condition that all paraxial rays starting from the source will converge at a point O on the axis. find the focal length

(ii) A gravitational lens may be assumed to have a varying width of the form show that an observer will see an image of a point object as a ring about the centre of the lens with an angular radius $\beta =\sqrt { \frac { (n-1){ k }_{ 1 }\frac { u }{ v } }{ u+v } }$

• 5)

A refracting telescope has an objective of focal length 1m  and an eye of the sun 10cm in diameter is formed at a distance of 24cm from eye piece.what angle does the sun subtend at the objective?

#### 12th Standard CBSE Physics - Electromagnetic Induction and Alternating Currents Five Mark Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

An LC circuit a 20 mH inductor and a $50\mu F$ capacitor with an initial charge of 10 mC. The resistance of the circuit is negligible. Let the instant the circuit is closed be t=0.
(a) What is the total energy stored initially? IS it conserved during LC oscillations?
(b) What is the natural frequency of the circuit?
(c)  At what time is the energy stored
(i) completely electrical (i.e., stored in the capacitor)?
(ii) completely magnetic (i.e., stored in the inductor).
(d) At what times is the total energy shared equally between the inductor and the capacitor?
(e) If a resistor is inserted in the circuit, how much energy is eventually dissipated as heat?

• 2)

Consider an infinitely long wire carrying a current I (t), with $\frac { dI }{ dt } =\lambda =constant.$ Find the current produced in the rectangular loop of wire ABCD if its resistance is R

• 3)

A rod of mass m and resistance R slides smoothly over two parallel perfectly conducting wires kept sloping at an angle $\theta$ with respect to the horizontal. The circuit is closed through a perfect conductor at the top. There is a constant magnetic field B along the vertical direction. If the rod is initially at rest, find the velocity of the rod as a function of time.

• 4)

State Lenz's law and illustrate it with experiment.

• 5)

What is the difference between electric field produced by stationary charges and moving charges?

#### 12th CBSE Physics - Magnetic Effects of Current Five Mark Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

A straight horizontal conducting rod of length 0.45m and mass 60g is suspended by two vertical wires at its ends.  A current of 5.0 A is set up in the rod though the wires.
(a) What magnetic field should be set up normal to the conductor in order that the tension in the wires is zero?
(b) What will be the total tension in the wires if the direction of current is reversed keeping the magnetic field same as before? (Ignore the mass of the wires.) g = 9.8 ms-2.

• 2)

How are materials classified according to their behaviour in magnetic field?

• 3)

Discuss the sensitivity of a moving coil galvanometer.

• 4)

Find the expression for maximum energy of a charged particle accelerated by a cyclotron.

• 5)

Explain using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of
(ii) soft iron core?
Also, define the terms
(iii) current sensitivity and
(iv) voltage sensitivity of a galvanometer.
Why does increasing the current sensitivity not necessarily increase voltage sensitivity?

#### 12th Standard CBSE Physics - Communication Systems Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

The length of a half wave dipole antenna is 0.5 m. Calculate the optimum transmission frequency.

• 2)

What should be the length of the dipole antenna for a carrier wave of frequency $3\times10^{ 8 }$Hz?

• 3)

A sinusoidal voltage amplitude modulates another sinusoidal voltage of amplitude 2 kV resulting in two side bands of amplitude 200 V. Find the modulation index.

• 4)

A band width of 5 MHz is available for AM transmission.If the maximum audio signal frequency used for modulating the carrier is not to exceed 5 kHz,how many stations can be broadcast within this band simultaneously without interfering with each other?

• 5)

In a diode detector,output circuit consisits of $R=1M\Omega$ and C=1 pF.Calculate the carrier frequency it can detect.

#### 12th Standard CBSE Physics - Electronic Devices Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the second has a voltage gain 20. If the input signal is 0.01 volt,Calculate the output ac.signal.

• 2)

In an n-type silicon, which of the following statement is true?
(a) Electrons are majority carriers and trivalent atoms are the dopants.
(b) Electrons are minority carriers and pentavalent atmos are the dopants.
(c) Holes are minority carriers and pentavalent atmos are the dopants.
(d) Holes are majority carriers and trivalent atmos are the dopants.

• 3)

For the transistor action, which of the following statements are correct?
(a) Base, emitter and collector regions should have similar size and doping concentrations
(b) The base region must be very thin and lightly doped
(c) The emitter junction is forward biased and collector junction is reverse biased.
(d) Both the emitter junction as well as the collector junction are forward biased.

• 4)

When an electronic field is applied across a semiconductor
(a) electrons move from lower energy level to lower energy level in the conduction band.
(b) electrons move from higher energy level to lower energy level in the conduction band.
(c) holes in the valence band move from higher energy level to lower energy level.
(d) holes in the valence band move from lower energy level to higher energy level

• 5)

To reduce the ripples in a rectifier circuit with capacitor filter
(a) $R_{ L }$ should be increased
(b) input frequency should be decreased.
(c) input frequency should be increased.
(d) Capacitors with high capacitance should be used.

#### 12th Standard CBSE Physics - Atoms and Nuclei Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

(a) Define the term decay constant and half life of a radioactive sample. Derive the relation connecting the two.
(b) How many disintegrations per second will occur in one gram of 92U238, if its half-life against alpha decay is $1.42\times { 10 }^{ 17 }s$ ?

• 2)

(a)Using the Bohr's model, calculate the speed of the electron in a hydrogen atom in the n=1,2, and 3 levels
(b)Calculate orbital period in each of these levels.

• 3)

What is the minimum energy that must b given to a H-atom in ground state so that it can angular momentum of the system is conserved, what would be the angular momentum of such H photon?

#### 12th Standard CBSE Physics - Dual Nature of Radiation and Matter Three Marks - by Sharma - Kochi - View & Read

• 1)

Deine the term:
(a)(i)Work function (ii)threshold frequency and(iii)stopping potential with reference to photoelectric effect
(b)Calculate the maximum kinetic energy of electrons emitted from a photosensitive surface of work function 3.2 eV for the incident radiation of wavelength 300 nm.

• 2)

The energy flux of sunlight reaching the surface of the earth is.$1.388\times{ 10 }^{ 3 }w/{ m }^{ 2 }$. How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.

• 3)

Estimating the following two numbers should be interesting. The first number will tell you why radio engineers do not need to worry much about photons. The second number tells you why our eye can never count photons,even in barely detectable light.
(a) The number of photons emitted per second by an MW transmitter of 10 kW power emitting radio waves of wavelength 500 m.
(b)The number of photons entering the pupil of our eye per second corresponding to the minimum intensity of while light that we humans can perceive ($\sim$${ (10 }^{ -10 }Wm^{ -2 })$ .Take the area of the pupil to be white light to be about 0.4 cm2and the average frequency of white light to be about 6 x 1014 Hz.

• 4)

(a)Quarks inside protons and neutrons are thought to carry fractional charges $\left( +\frac { 2 }{ 3 } e,-\frac { 1 }{ 3 } e \right) .$ Why do they not show up in Millikan's oil drop experiment?
(b) What is so special about the combination elm? Why do we not simply talk of e and $m$ specially?
(c) Why should gases be insulators at ordinary pressure and start conducting at very low pressure.
(d) Every metal has a definite work function, Why do photoelectrons not come out all with same energy if incident radiations is monochromatic?Why is there an energy distribution of photoelectrons?
(e) The energy and momentum of an electron are related to the frequency and wavelength of the associated matter wave by the relations :$E=hv,p=\frac { h }{ \lambda }$
But while the value of  $\lambda$ is physically significant , the value of $v$ (and therefore the value of the phase speed $v\lambda$ ) has no physical significance. Why?

#### 12th Standard CBSE Physics - Wave Optics Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

A double convex lens made of glass of refractive index 1.5 has both radii of curvature of magnitude 20 cm. An object 2 cm high is placed at 10 cm from the lems. Find the position, nature and size of the image.

• 2)

In the normal adjustment of an astronomical telescope, the distance between the objective lens and the eye lens is 10 sm. The magnifying power of the telescope is 4. Calculate the focal lengths of objective and eye lens.

• 3)

A breaker is filled with water to a height of 12.5 cm. The apparent depth of a needle lying at the bottom of the beaker is measured by a microscope to be 9.4 cm. What is the refractive index of water ? If  water is If water is replaced by a liquid of refractive index 1.63 upto the same height, by what distance would the microscope have to be moved to focus on the needle again ?

• 4)

Explain how corpuscular theory predicts the speed of light in a medium, say water, is greater than the speed of light in vacuum. Is the prediction confirmed by experimental determination of the speed of light in water? If not, which alternative picture of light is consistent with experiment?

#### CBSE 12th Physics - Electromagnetic Waves Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

Suppose that the electric field part of an electromagnetic wave in vacuum is
$\overrightarrow { E } =\left\{ \left( 3.1N/C \right) \cos { \left[ \left( 1.8㎭/m \right) y+\left( 5.4\times { 10 }^{ 6 }㎭-{ s }^{ -1 }t \right) \right] } \right\} \hat { i }$
(a) What is the direction of propagation?
(b) What is the wavelength $\lambda$?
(c) What is the frequency $v$ ?
(d) What is the amplitude of the magnetic field part of the wave?
(e) Write an expression for the magnetic field part of the wave.

• 2)

About 5% of the power of a 100 W light bulb is converted to visible radiation. What is the average intensity of visible radiation.
(a) At a distance of 1 m from the bulb
(b) At a distance of 10 m?
Assume that the radiation is emitted isotropically and neglect reflection.

• 3)

Monica's mother was heating food on a gas stove. Her friend Ruchi came and saw her mother heating food on the gas stove. Ruchi told Monica's mother, "Why don't you buy a microwave oven"? Monica's mother replied at once that she doesn't like to use microwave oven. Monica and Ruchi made it clear that microwave is not harmful for cooking food. This is an easy and safe process. Monica's mother got convinced and ordered for a microwave oven. Monica's mother then arranged a small party for her friends and told them the advantages of a microwave oven.
What value was displayed by Monica and her friend?
What value was displayed by Monica to her friends?

• 4)

The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is B0 = 510 nT. What is the amplitude of the electric field part of the wave?

#### 12th Standard CBSE Physics - Current Electricity Five Mark Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

The galvanometer in the circuit shown here has a resistance of 20$\Omega$The terminals X and Y are connected to a cell of e.m.f. 1.5V and internal resistance 10$\Omega$ Calculate the current flowing in the galvanometer:
(i) When the switch S is in position.
(ii) When the switch S is in position B.

• 2)

A battery of e.m.f. 10V and internal resistance $3\Omega$ is connected to a resistor. If the current in the circuit is 0.5A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?

• 3)

Kirchhoff's junction rule is a reflection of
(a) conservation of current density vector.
(b) conservation of charge
(c) the fact that the momentum with which a charged particle approaches a junction is unchanged as the charged particle leaves the junction.
(d) the fact that there is no accumulation of charges at a junction.

• 4)

(a) Define electric current. What is its S.I. unit? Is it a scalar or a vector quantity? What is the direction of electric current?
(b) How many electrons flowing per second should flow to produce a current of 1A?

• 5)

(a) State Ohm's law.
(b) Define resistance. Give its SI unit.

#### 12th CBSE Physics - Electrostatics Five Mark Question Paper - by Renuka Thirupasur - Vadodara - View & Read

• 1)

How rubbing of the two bodies produces electricity?

• 2)

Define electric field at a point.An electron moves a distance of 6.0cm when accelerated from rest by an electric field of strength $2\times {{10}^{4}} N{{C}^{-1}}$.Calculate the times of travel.

• 3)

(i) Explain, using suitable diagram,  the  difference in the behaviour of a
(a) conductor
(b) dielectric in the presence of external electric field. Define the terms polarisation of a dielectric and write its relation with susceptibility.
(ii) A thin metallic spherical shell of radius R carries a charge Q on its surface. A point charge Q/2 is placed at its centre C and an another charge +2Q is placed outside the shell at a distance x from the centre as shown in figure. Find
(a) the force on the charge at the centre of the shell and at point A,
(b) the electric flux through the shell.

• 4)

The electric field at a point on the axial line at a distance of 10 cm from the center of an electric dipole is 3.75$\times$ N/C.Calculate the length of an electric dipole.

• 5)

(i) Three equal charges, each equal to q are placed at the three corners of square of side $\alpha$ .Find the electric field at the fourth corner.
(ii) Find the electric field at the point P in figure given below.

#### 12th Standard CBSE Physics - Magnetic Effects of Current Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

A uniform magnetic field of 1.5 T exists in a cylindrical region of radius 10.0 cm, its direction is parallel to the axis along east to west.  A wire carrying current of 7.0 A in the north to south direction passes through this region.  What is the magnitude and direction of the force on the wire if,
(a) the wire intersects the axis,
(b) the wire is turned from N-S to northeast-southwest direction,
(c) the wire in the N-S direction is lowered from the axis by a distance of 6.0 cm?

• 2)

A circular coil of 20 turns and radius 10 cm is placed in a uniform magnetic field of 0.10 T normal to the plane of the coil.  If the current in the coil is 5.0 A, what is the
(a) total torque on the coil,
(b) total force on the coil,
(c) average force on each electron in the coil due to the magnetic field?
(The coil is made of copper wire of cross-sectional area 10-5 m2, and the free electron density in copper is given to be about 1029 m-3)

• 3)

A long straight horizontal cable carries a current of 2.5A in the direction 10o south of west to 10o north of east. The magnetic meridian of the place happens to be 10o west of the geographic meridian, The earth's magnetic field at the location is 0.33G, and the angle of dip is zero. Locate the line of neutral points(Ignore the thickness of the cable).

• 4)

A compass needle free to turn in a horizontal plane is placed at the centre of circular coil of 30 turns and radius 12cm. The coil is in a vertical plane making an angle of 45o with the magnetic meridian. When the current in the coil is 0.35A, the needle points west to east
(a) Determine the horizontal component of the earth's magnetic field at the location.
(b) The current in the coil is reserved and the coil is rotated about its vertical axis by an angle of 90in the anticlockwise sense looking from above. Predict the direction of the needle. Take the magnetic declination at the place to be zero.

• 5)

A closely wound solenoid of 2000 turns and area of cross-section 1.6 x 10-4mcarrying a current of 4.0A is suspended through its centre allowing it to turn in a horizontal plane.
(a) What is the magnetic moment associated with the solenoid?
(b) What is the force and torque on the solenoid if a uniform horizontal magnetic field of 7.5 x 10-2T is set up at an angle of 30with the axis of the solenoid?

#### 12th Standard CBSE Physics - Electromagnetic Induction and Alternating Currents Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

A series LCR circuit with $R=20\Omega$ , L=1.5H and $C=35\mu F$ is connected to a variable frequency 200 V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?

• 2)

A coil of inductance 0.50H and resistance $100\Omega$ is connected to a 240V, 50 Hz ac supply.
(a) What is the maximum current in the coil?
(b) What is the time lag between the voltage maximum and the current maximum?

• 3)

$100\mu F$ capacitor in series with a $40\Omega$ is connected to a 110 V, 60 Hz supply.
(a) What is the maximum current in the circuit?
(b) What is the time lag between the current maximum and the voltage maximum?

• 4)

Explain why the coils of the resistance box are wound over themselves.

#### CBSE 12th Physics - Current Electricity Three Marks Questions - by Sharma - Kochi - View & Read

• 1)

Figure shows a potentiometer with a cell of 2.0V and internal resistance of 0.40$\Omega$ maintaining a potential drop across the resistor wire AB. A standard cell which maintains a constant emf of 1.02V (for very moderate currents upto a few mA) gives a balance point at 67.3 cm length of the wire. To ensure very low currents drawn from the standard cell a very high resistance 600k$\Omega$ is put in series with it Which is shorted cell is then replaced by a cell of unknown emf E and the balance point found similarly, turns out to be at 82.3 cm length of the wire.

(a) What is the value E?
(b) What purpose does the high resistance o 600k$\Omega$ have?
(c) Is the balance point affected by this high resistance?
(d) Is the balance point affected by the internal resistance of 600k$\Omega$ have?
(e) Would the method work in the above situation if the driver cell of the potentiometer had an emf of 1.0V instead of 2.V?
(f) Would the circuit work well for determining an etremely small emf say of the order of a few mV (such as the typical emf of a thermo-couple)? If not how will you modiy the circuit?

• 2)

A dc supply of 120V  is connected to a large resistance X. A voltmeter of resistance 10k$\Omega$placed in series in the circuit reads 4V. What is the value of X? What so you think is the purpose in using a voltmeter instead of an ammeter to determine the large resistance X?

• 3)

(a) Three resistors $1\Omega ,2\Omega \ and\ 3\Omega$ are combined in series. What is the total resistance of the combination?
(b) If the combination is connected to a battery of emf 12 V and negligible internal resistance, obtain the potential drop across each resistor.

• 4)

(a) Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance are joined in series to provide a supply to a resistance of $8.5\Omega$ . What are the currents drawn from the supply, and its terminal voltage? (b) A secondary cell after long use has an emf 1.9 V and a large internal resistance of $380\Omega$. What maximum current can be drawn from the cell? Could the cell drive the starting motor of a car?

• 5)

(a) A steady current flows in a metallic conductor of non-uniform cross-section. Say which of these quantities is constant along the conductor current density, electric field, drift speed?
(b) Is Ohm's law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm's law.
(c) A low voltage supply from which one needs high currents must have very low internal resistance. Why?
(d) A high tension (HT) supply of say 6kV must have a very large internal resistance. Why?

### CBSE Education Study Materials

#### 12th CBSE Physics 2019 - 2020 Academic Syllabus - by Sharma - Kochi Aug 21, 2019 Aug 21, 2019

Physics 2019 - 2020 Academic Syllabus

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#### CBSEStudy Material - Sample Question Papers with Solutions for Class 12 Session 2020 - 2021

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