Download CBSE Class 12th Standard CBSE Physics question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Physics

Questions:

Multiple Choice Question

91 x 1 = 91

The electric field at a point is

(a)

always continuous

(b)

continuous if there is no charge at that point

(c)

discontinuous only if there is a negative charge at that point

(d)

discontinuous if there is a charge at that point

If \(\oint _{ s }^{ }{ E.ds } =0\) over a surface, then

(a)

the electric field inside the surface and on it is zero

(b)

the electric field inside the surface is necessarily uniorm

(c)

the number of flux lines entering the surface must be equal to the number of flux lines leaving it

(d)

all charges must necessarily be outside the surface

A condenser is charged to double its initial potential. The energy stored in the condenser becomes x times, where x =

(a)

(b)

(c)

(d)

1/2

Charge on a capacitor is doubled. Its capacity becomes k times, where

(a)

k = 2

(b)

k = 1

(c)

k = \(1\over 2\)

(d)

k = 4

A 50Hz AC current of crest value 1A flows through the primary of a transformer. If the mutual inductance between the primary and secondary be 0.5 H, the creast voltage induced in the secondary is

(a)

75 V

(b)

150 V

(c)

100 V

(d)

none of these

A conducting circuit loop is placed in a uniform magnetic field of induction B tesla with its plane normal to the field. Now, the radius of the loop starts sharinking at the rate dr/dt. The induced emf at the instant when the radius is R is:

(a)

\(\pi rB\left( \frac { dr }{ dt } \right) \)

(b)

\(2\pi rB\left( \frac { dr }{ dt } \right) \)

(c)

\(\pi r^{ 2 }\left( \frac { dr }{ dt } \right) \)

(d)

\(\left( \frac { \pi r^{ 2 } }{ 2 } \right) ^{ 2 }\left( \frac { dr }{ dt } \right) \)

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

(a)

\(\frac { B\pi { r }^{ 2 }\omega }{ 2R } \)

(b)

\(\frac { \left( B\pi { r }^{ 2 }\omega \right) ^{ 2 } }{ 8R } \)

(c)

\(\frac { \left( B\pi { r }\omega \right) ^{ 2 } }{ 2R } \)

(d)

\(\frac { \left( B\pi { r^{ 2 } }\omega \right) ^{ 2 } }{ 8R } \)

A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields \(\vec { E } \quad and\quad \vec { B } \) with a velocity \(\vec { \upsilon } \) perpendicular to both \(\vec { E } \quad and\quad \vec { B } ,\) and comes out without any change in magnitude or direction of \(\vec { \upsilon } .\) Then

(a)

\(\vec { \upsilon } =\vec { B } \times \vec { E } /{ E }^{ 2 }\)

(b)

\(\vec { \upsilon } =\vec { E } \times \vec { B } /{ B }^{ 2 }\)

(c)

\(\vec { \upsilon } =\vec { B } \times \vec { E } /{ B }^{ 2 }\)

(d)

\(\vec { \upsilon } =\vec { E } \times \vec { B } /{ E }^{ 2 }\)

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

(a)

E/B

(b)

E/qB

(c)

2 mE/qB

(d)

\(m{ E }^{ 2 }/2q{ B }^{ 2 }\)

10.

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

(a)

1/2

(b)

1/4

(c)

(d)

11.

The distiction between conductors, insulators and semiconductors is largely connected with

(a)

the type of crystal lattice

(b)

binding energy of their electrons

(c)

relative width of their energy gap

(d)

their ability to conduct current

12.

The decimal equivalent of the binary number \((11010.101)_{ 2 }\) is

(a)

17+9.625

(b)

15+9.625

(c)

26+0.625

(d)

24+0.625

13.

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 \(\phi \).

(a)

Here, the power factor cos \(\phi \ge 0,\ P\ge 0\)

(b)

The driving force can given no energy to the oscillator (P = 0) in some cases

(c)

The driving force can not syphon out (P<0) the energy out of oscillator

(d)

The driving force can take away energy out of the oscillator

14.

Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?

(a)

R = 20\(\Omega \), L = 1.5H, C = 35\(\mu\)F

(b)

R = 25\(\Omega \), L = 2.5H, C = 45\(\mu\)F

(c)

R = 15\(\Omega \), L = 3.5H, C = 30\(\mu\)F

(d)

R = 25\(\Omega \), L = 1.5H, C = 45\(\mu\)F

15.

To reduce the reasonant frequency in an LCR series circuit with a generator

(a)

the generator frequency should be reduced

(b)

another capacitor should be added in parallel to the first

(c)

the iron core of the inductor should be removed

(d)

dielectric in the capacitor should be removed

16.

In a common-emitter configuration, a transistor \(\beta =50\) and input resistance \(1k\ \Omega \) if the peak value of a.c.input is 0.01 V then the peak value of collector currents is

(a)

\(0.01\mu A\)

(b)

\(0.25\mu A\)

(c)

\(100 \ \mu A\)

(d)

\(10 \ \mu A\)

17.

An amplifier has a voltage gain \({ A }_{ v }=1000\). The voltage gain in \(db\) is

(a)

30 db

(b)

60 db

(c)

3 db

(d)

20 db

18.

An e.m.f. is produced in a coil, which is not connected to an external voltage source. This can be due to

(a)

the coil being in a time varying magnetic field

(b)

the coil moving in a time varying magnetic field

(c)

the coil moving in a constant magnetic field

(d)

the coil is stationary in external spatially varying magnetic field, which does not change with time

19.

A metal plate is getting heated. It can be because

(a)

a direct current is passing through the plate

(b)

it is placed in a time varying magnetic field

(c)

it is placed in a space varying magnetic field, but does not vary with time

(d)

a current is passing through the plate

20.

The current voltage relation of diode is given by \(I=(e^{ 1000V/T }-1)\) mA, where the applied V is n volts and the temperature T is in degree kelvin. If a students makes an error measuring \(\pm 0.01V\) while measuring the current of 5 mA at 300 K, what will be the error in the value of current in mA?

(a)

0.5 mA

(b)

0.05 mA

(c)

0.2 mA

(d)

0.02 mA

21.

When a momentum point source of light is at a distance of 0.2m front a photoelectric cell, the cutoff voltage and the saturation current are respectively 0.6V and 18.0 mA. If the same source is placed 0.6m away from the photoelectric cell, then

(a)

the stopping potential will be 0.2 volt

(b)

the stopping potential will be 0.6 volt

(c)

the saturation current will be 6.0 mA

(d)

the saturation current will be 2.0 mA

22.

An electron and proton have the same de-Broglie wavelength. The K.E of the electron is

(a)

zero

(b)

infinity

(c)

equal to K.E of the proton

(d)

greater than K.E. of proton

23.

What focal length should be reading spectacles have for a person whose near point is 50 cm?

(a)

25 cm

(b)

50 cm

(c)

-50 cm

(d)

-25 cm

24.

Mobilities of electrons and holes in a sample of intrinsic germanium at room temperature are \(0.36{ m }^{ 2 }{ v }^{ -1 }s^{ -1 } \ and \ 0.17 \ { m }^{ 2 }{ v }^{ -1 }s^{ -1 }\)The electron and hole densities are each equal to \(2.5 \times 10^{ 19 }m^{ -3 }\) .The electrical conductivity of germanium is

(a)

0.47 \(Sm^{ -1 }\)

(b)

1.09 \(Sm^{ -1 }\)

(c)

2.12 \(Sm^{ -1 }\)

(d)

4.24 \(Sm^{ -1 }\)

25.

A Ge specimen is doped with AI. The concentration of acceptor atoms is \(-10^{ 21 }\) atoms/\(m^{ 3 }\) , the concentration of electrons in the specimen is

(a)

\(10^{ 17 }/m^{ 3 }\)

(b)

\(10^{ 15 }/m^{ 3 }\)

(c)

\(10^{ 4 }/m^{ 3 }\)

(d)

\(10^{ 2 }/m^{ 3 }\)

26.

\({ \lambda }_{ e },{ \lambda }_{ p }\)and \({ \lambda }_{ \alpha }\)are the de-Broglie wavelengths of electron, proton and \(\alpha \) particle. If all are accelerated by potential, then

(a)

\({ \lambda }_{ e },{ <\lambda }_{ p }<{ \lambda }_{ \alpha }\)

(b)

\({ \lambda }_{ e },{ <\lambda }_{ p }>{ \lambda }_{ \alpha }\)

(c)

\({ \lambda }_{ e },{ >\lambda }_{ p }<{ \lambda }_{ \alpha }\)

(d)

\({ \lambda }_{ e },{ =\lambda }_{ p }>{ \lambda }_{ \alpha }\)

(e)

\({ \lambda }_{ e },{ >\lambda }_{ p }>{ \lambda }_{ \alpha }\)

27.

An electric field is applied to a semi-conductor Let the number of charge carriers be n and the average drift speed be v. If the temperature is increased

(a)

both n and v will decrease

(b)

both n and v will increase

(c)

n will increase but v will decrease

(d)

v will increase but n will decrease

28.

As the mass number 'A' increases, which of the following quantities related to nucleus do not change?

(a)

mass

(b)

volume

(c)

density

(d)

binding energy

29.

The de-Broglie wavelength of a particle moving with a velocity \(2.25\times { 10 }^{ 8 }m/s\)is equal to the wavelength of photon. The ratio of kinetic energy of a particle to the energy of the photon is (velocity of light is \(3\times { 10 }^{ 8 }m/s\))

(a)

1/8

(b)

3/8

(c)

5/8

(d)

7/8

30.

The kinetic energy of an electron gets quadrupled then the de-Broglie wavelength associated with it changes by the factor.

(a)

1/4

(b)

(c)

1/2

(d)

31.

A battery of 12V is connected to primary of a transformer with turns ratio n_s/n_p= 10. Voltage across secondary would by

(a)

120 V

(b)

1.3 V

(c)

12 V

(d)

Zero

32.

The relation \(\frac { { E }_{ s } }{ { E }_{ p } } =\frac { { n }_{ s } }{ { n }_{ p } } \) is applied only to

(a)

a.c. generator

(b)

d.c. generator

(c)

induction coil

(d)

step up/step down transformer

33.

The value of absolute electrical permittivity of free space is

(a)

\(9\times 10^9Nm^2C^{-2}\)

(b)

\(9\times 10^{-9}Nm^2C^{-2}\)

(c)

\(8.85\times 10^{-12}C^2N^{-1}m^{-2}\)

(d)

\(8.85\times 10^{-12}C^2Nm^{-2}\)

34.

The cause of charging is actual transfer of protons

(a)

actual transfer of protons

(b)

actual transfer of electrons

(c)

actual transfer of neutrons

(d)

none of the above

35.

Which of the following is not an insulator?

(a)

glass

(b)

rubber

(c)

ebonite

(d)

human body

36.

A small link dot on a paper is seen through a glass slab of thickness 4 cm and refractive index 1.5. The dot appears to be raised by

(a)

1 cm

(b)

2 cm

(c)

3 cm

(d)

1.33 cm

37.

A long solenoid has n turns per metre and current I A is flowing through it. The magnetic field induction at the ends of the solenoid is

(a)

zero

(b)

\({ \mu }_{ o }nI/2\)

(c)

\({ \mu }_{ o }nI\)

(d)

\(2{ \mu }_{ o }NI\)

38.

A circular coil carrying current behaves as a

(a)

bar magnet

(b)

horse shoe magnet

(c)

magnetic shell

(d)

solenoid

39.

In single slit diffraction pattern, how does the width of central maximum change when light of smaller wavelength is used?

(a)

decreases

(b)

increases

(c)

remains unaffected

(d)

cannot be predicted

40.

A closed surface in vacuum encloses charges -q and +3q. Another charge -2q lies outside the surface. Total electric flux over the surface is

(a)

Zero

(b)

\(2 q\over \epsilon_o\)

(c)

\(-{3q\over \epsilon_o}\)

(d)

\(4q\over\epsilon_o\)

41.

A sodium lamp emits \(3.14\times { 10 }^{ 20 }\)photons per second. Calculate the distance from sodium lamp where flux of photon is one photon per second per cm².

(a)

\({ 10 }^{ 10 }cm\)

(b)

\(5\times { 10 }^{ 9 }cm\)

(c)

\(5\times { 10 }^{ 8 }cm\)

(d)

\({ 10 }^{ 9 }cm\)

42.

The wavelength of a KeV photon is \(1.24\times { 10 }^{ -9 }m\). What is the frequency of 1 MeV photon?

(a)

\(1.24\times { 10 }^{ 15 }Hz\)

(b)

\(2.4\times { 10 }^{ 20 }Hz\)

(c)

\(1.24\times { 10 }^{ 18 }Hz\)

(d)

\(2.4\times { 10 }^{ 23 }Hz\)

43.

Which of the following cannot be polarized?

(a)

X-rays

(b)

radio waves

(c)

sound waves

(d)

light waves

44.

Polarizing angle for a medium is \(60°\) . Its refractive index is

(a)

1.732

(b)

(c)

1.414

(d)

45.

When an electric field is applied across a semiconductor

(a)

electrons move from lower energy level to higher energy level in the condition 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.

46.

Potential energy of an electric dipole held at an angle \(\theta\) in a uniform electric field is zero when \(\theta=\)

(a)

\(0^o\)

(b)

90^o

(c)

180^o

(d)

360^o

47.

Electric dipole moment is

(a)

scalar

(b)

neither scalar vector

(c)

a vector directed from -q to +q

(d)

a vector directed from +q to -q

48.

Monochromatic light of frequency f₁ incident on a photocell and the stopping potential is found to be V₁. What is the new stopping potential of the cell if it radiated by monochromatic light of frequency f₂?

(a)

\({ V }_{ 1 }-\frac { h }{ e } ({ f }_{ 2 }-{ f }_{ 1 })\)

(b)

\({ V }_{ 1 }+\frac { h }{ e } ({ f }_{ 2 }+{ f }_{ 1 })\)

(c)

\({ V }_{ 1 }-\frac { h }{ e } ({ f }_{ 2 }+{ f }_{ 1 })\)

(d)

\({ V }_{ 1 }+\frac { h }{ e } ({ f }_{ 2 }-{ f }_{ 1 })\)

49.

If \({ \lambda }_{ Cu }\) is the wavelength of \({ K }_{ \alpha }\) X-ray line of copper (atomic number 29) and \({ \lambda }_{ Mo }\) is the wavelength of the \({ K }_{ \alpha }\) X-ray line of molybdenum (atomic number 42), then the ratio \({ \lambda }_{ Cu }/{ \lambda }_{ Mo }\) is close to

(a)

1.99

(b)

2.14

(c)

0.50

(d)

0.48

50.

In a photoemissive cell, with exciting wavelength \(\lambda \)the fastest electron has speed v. If the exciting wavelength is changed to \(\frac { 3\lambda }{ 4 } \), the speed of the fastest electron will be

(a)

\(v{ \left( \frac { 3 }{ 4 } \right) }^{ 1/2 }\)

(b)

\(v{ \left( \frac { 4 }{ 3 } \right) }^{ 1/2 }\)

(c)

\(less than \ v{ \left( \frac { 3 }{ 4 } \right) }^{ 1/2 }\)

(d)

\(greater than \ v{ \left( \frac { 3 }{ 4 } \right) }^{ 1/2 }\)

51.

If K₁ and K₂ are maximum kinetic energies of photoelectrons emitted when light of wavelength \({ \lambda }_{ 1 }\)and \({ \lambda }_{ 2 }\)respectively are incident on a metallic surface.If \({ \lambda }_{ 1 }=3{ \lambda }_{ 2 }\)

(a)

\({ K }_{ 1 }>\left( \frac { { K }_{ 2 } }{ 3 } \right) \)

(b)

\({ K }_{ 1 }<\left( \frac { { K }_{ 2 } }{ 3 } \right) \)

(c)

\({ K }_{ 1 }={ 3K }_{ 2 }\)

(d)

\({ K }_{ 2 }={ 3K }_{ 1 }\)

52.

When a metallic is illuminated with radiation of wavelength \(\lambda \) , the stopping potential is V.If the same surface is illuminated with radiation of wavelength, \(2\lambda \) the stopping potential is V/4. The threshold wavelength for the metallic surface is

(a)

\(4\lambda \)

(b)

\(5\lambda \)

(c)

\(5\lambda /2\)

(d)

\(3\lambda \)

53.

Light of wavelength \(6000 \ \overset { \circ }{ A } \) falls on a plane reflecting surface. The reflected wavelength is

(a)

\(6000 \ \overset { \circ }{ A } \)

(b)

\(<6000 \ \overset { \circ }{ A } \)

(c)

\(>6000 \ \overset { \circ }{ A } \)

(d)

cannot say

54.

Image of an object in a concave mirror is

(a)

always real

(b)

always virtual

(c)

always erect

(d)

real or virtual depending on position of object

55.

The ratio of the speed of an object to the speed of its real image of magnification m in the case of a convex mirror is

(a)

\(-\frac { 1 }{ { m }^{ 2 } } \)

(b)

\({ m }^{ 2 }\)

(c)

-xm

(d)

\(\frac { 1 }{ { m } } \)

56.

For light diverging from a point source

(a)

The wavefront is spherical

(b)

The intensity decrease in proportion to the distance squared

(c)

The wavefront is parabolic

(d)

The intensity at the wavefront does not depend on the distance

57.

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

(a)

There shall be alternate interference pattern of red and blue

(b)

There shall be alternate interference pattern of red distinct from that for blue

(c)

There shall be no interference fringes

(d)

There shall be alternate interference pattern of red mixing with one for blue

58.

The total energy of electron in the ground state of hydrogen atom is - 13.6 eV. The K.E. of this electron in first excited state is

(a)

6.8 eV

(b)

13.6 eV

(c)

1.7 eV

(d)

3.4 eV

59.

The transistor is operated in common emitter configuration at \(\mu A\) to 200 \(\mu A\) produces a change in the collector current from 5 mA to 10 mA. The current gain is

(a)

100

(b)

150

(c)

(d)

60.

Q factor of resonance is given by

(a)

\(\frac { 1 }{ R } \sqrt { \frac { L }{ C } } \)

(b)

\(\frac { 1 }{ R } \sqrt { \frac { C }{ L } } \)

(c)

\(\frac { 1 }{ L } \sqrt { \frac { R }{ C } } \)

(d)

\(\frac { 1 }{ C } \sqrt { \frac { L }{ R } } \)

61.

The electrical resistance of depletion layer is large because

(a)

it has no charge carriers

(b)

it has few holes as charge carriers

(c)

it contains few electrons as charge carriers

(d)

it contains few ions as charge carriers

62.

In the middle of the depletion layer of a review biased p-n junction, the

(a)

electric field is zero

(b)

potential is zero

(c)

electric field is maximum

(d)

potential is maximum

63.

If \({ m }_{ e }\)is mass of an electron, then mass of pion plus particle if

(a)

207\({ m }_{ e }\)

(b)

273\({ m }_{ e }\)

(c)

\(\frac { { m }_{ e } }{ 207 } \)

(d)

\(\frac { { m }_{ e } }{ 273 } \)

64.

Which of the following communication system has maximum band width?

(a)

Optical fibre communication

(b)

Skywave communication

(c)

Line communication

(d)

Statellite communication

65.

From which layer of atmosphere, the radiowaves are reflected?

(a)

Ionosphere

(b)

Chromosphere

(c)

Mesosphere

(d)

None

66.

Minimum number of geostationary satellites needed for satellite communication is

(a)

(b)

(c)

(d)

67.

Which of the following is not an electromagnetic wave?

(a)

X-rays

(b)

UV rays

(c)

sound waves

(d)

radio waves

68.

Which of the following maxwell equation have a source of \(\overset { \rightarrow }{ E } \) and \(\overset { \rightarrow }{ B } \) ?

(a)

\(\oint { \overset { \rightarrow }{ E } .\overset { \rightarrow }{ ds } } =\frac { q }{ { \epsilon }_{ 0 } } \)

(b)

\(\oint { \overset { \rightarrow }{ B } .\overset { \rightarrow }{ dl } } ={ \mu }_{ 0 }l+{ \mu }_{ 0 }{ \epsilon }_{ 0 }\frac { d }{ dt } \oint { \overset { \rightarrow }{ E } .\overset { \rightarrow }{ ds } } \)

(c)

\(\oint { \overset { \rightarrow }{ E } .\overset { \rightarrow }{ dl } } =-\frac { d }{ dt } \oint { \overset { \rightarrow }{ B } .\overset { \rightarrow }{ ds } } \)

(d)

\(\oint { \overset { \rightarrow }{ B } .\overset { \rightarrow }{ ds } } =0\)

69.

The conduction band in a solid is partially filled at 0 k. The solid sample is

(a)

Conductor

(b)

Semiconductor

(c)

Insulator

(d)

none of these

70.

If \({ u }_{ E },{ u }_{ m }\) are the energy density of electromagnetic wave due to electric and magnetic field vectors, \({ E }_{ rms },{ B }_{ rms }\) are the rms value of electric and magnetic field vectors in an electromagnetic wave. then the total energy density of a sinusoidal electromagnetic wave is

(a)

\({ u }_{ E }\)

(b)

\({ u }_{ E }{ +u }_{ m }\)

(c)

\(\frac { 1 }{ 2 } { \epsilon }_{ 0 }{ E }_{ rms }^{ 2 }+\frac { { E }_{ rms }^{ 2 } }{ { 2\mu }_{ 0 } } \)

(d)

\(\frac { 1 }{ 2 } { \epsilon }_{ 0 }{ E }_{ 0 }^{ 2 }+\frac { 1 }{ 2 } \frac { { E }_{ 0 }^{ 2 } }{ { \mu }_{ 0 } } \)

71.

Two photons, each of energy 2.5eV are simultaneously incident on the metal surface. If the work function of the metal is 4.5eV, then from the surface of metal

(a)

one electron will be emitted with energy 0.5eV

(b)

two electrons will be emitted with energy 0.25eV

(c)

more than two electrons will be emitted

(d)

not a single electron will be emitted.

72.

A device that connects one computer to another across ordinary telephone lines is called

(a)

transducer

(b)

fax

(c)

modem

(d)

none of the above

73.

If \(\lambda \) is wavelength of radio signals to be transmitted, then the length of Hertz antenna is

(a)

\(\lambda \)

(b)

\(\frac { \lambda }{ 4 } \)

(c)

\(\frac { \lambda }{ 2 } \)

(d)

\(2\lambda\)

74.

The audible range of frequencies is

(a)

20 kHz to 20 MHz

(b)

20 Hz to 20 kHz

(c)

20 Hz to 20 MHz

(d)

none of the above

75.

The disturbance or distortion in the transmission and processing of message signals is called

(a)

noise

(b)

attenuation

(c)

interference

(d)

none of these

76.

The correct option if in vacuum the speed of gamma rays, x-rays and microwaves are \({ v }_{ g }, \ { v }_{ x }and \ { v }_{ m }\)

(a)

\({ v }_{ g }<{ v }_{ x }<{ v }_{ m }\)

(b)

\({ v }_{ g }<{ v }_{ x }>{ v }_{ m }\)

(c)

\({ v }_{ g }>{ v }_{ x }>{ v }_{ m }\)

(d)

\({ v }_{ g }={ v }_{ x }={ v }_{ m }\)

77.

A red LED emits light of 0.1 watts uniformly around it. The amplitude of the electric field of the light at a distance of 1 m from the diode is

(a)

1.73 V/m

(b)

2.45 V/m

(c)

5.48 V/m

(d)

7.75 V/m

78.

An electromagnetic wave in a vacuum has the electric and magnetic field \(\overset { \rightarrow }{ E } \) and \(\overset { \rightarrow }{ B } \). which are always perpendicular to each other. The direction of polarization is given by \(\overset { \rightarrow }{ X } \) and that of wave propagation by \(\overset { \rightarrow }{ K } \) . Then:

(a)

\(\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ B } \ and \ \overset { \rightarrow }{ K } \parallel \overset { \rightarrow }{ B } \times \overset { \rightarrow }{ E } \)

(b)

\(\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ E } \ and \ \overset { \rightarrow }{ K } \parallel \overset { \rightarrow }{ E } \times \overset { \rightarrow }{ B } \)

(c)

\(\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ B } \ and \ \overset { \rightarrow }{ K } \parallel \overset { \rightarrow }{ E } \times \overset { \rightarrow }{ B } \)

(d)

\(\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ E } \ and \ \overset { \rightarrow }{ K } \parallel \overset { \rightarrow }{ B } \times \overset { \rightarrow }{ E } \)

79.

In an electromagnetic wave, electric and magnetic fields are 200 V/m and 0.365 A/m. The maximum rate of energy flow is

(a)

\(73.0 \ W/{ m }^{ 2 }\)

(b)

\(36.5 \ W/{ m }^{ 2 }\)

(c)

\(54.7 \ W{ /m }^{ 2 }\)

(d)

\(77.8 \ W/{ m }^{ 2 }\)

80.

The refractive index and the permeability of a medium are respectively 1.5 and \(5\times { 10 }^{ -7 }H{ m }^{ -1 }\). The relative permittivity of the medium is nearly

(a)

(b)

(c)

(d)

(e)

81.

When number of turns of a soleniod is doubled, its self inductance becomes k times, where k =

(a)

(b)

(c)

(d)

82.

Which one is not an application of eddy currents?

(a)

Magnetic brakes

(b)

speedometers

(c)

Induction furnace

(d)

Transformers

83.

In the relation \(\phi \) = BA cos \(\theta \), \(\theta \) is angle........

(a)

which normal to surface area makes with the direction of magnetic field

(b)

which magnetic field makes with the surface

(c)

which is never constant

(d)

none of the above

84.

A charged particle oscillates about its mean equilibrium position with a frequency of 10⁹ Hz. What is the frequency of electromagnetic waves produced by the oscillator?

(a)

will have frequency of 10⁹ Hz

(b)

will have frequency of 2 x 10⁹ Hz

(c)

will have a wavelength of 0.3 m

(d)

fall in the region of radiowaves

85.

The velocity of light in vacuum can be changed by changing

(a)

frequency

(b)

amplitude

(c)

wavelength

(d)

none of these

86.

An electron (mass m) with an initial velocity \(v={ v }_{ 0 }\vec { i } \) is in an electric field \(E={ E }_{ 0 }\vec { j } E={ E }_{ 0 }\vec { j } \) . If \(\lambda =\frac { h }{ m{ v }_{ 0 } } \) its de-Broglie wavelength at time t is given by

(a)

\({ \lambda }_{ 0 }\)

(b)

\({ \lambda }_{ 0 }\sqrt { 1+\frac { { e }^{ 2 }{ E }_{ 0 }^{ 2 }\quad { t }^{ 2 } }{ { m }^{ 2 }{ v }_{ 0 }^{ 2 } } } \)

(c)

\(\frac { { \lambda }_{ 0 } }{ \sqrt { 1+\frac { { e }^{ 2 }{ E }^{ 2 }{ t }^{ 2 } }{ { m }^{ 2 }{ { v }_{ 0 }^{ 2 } } } } } \)

(d)

\(\frac { { \lambda }_{ 0 } }{ \sqrt { 1+\frac { { e }^{ 2 }{ E }^{ 2 }{ t }^{ 2 } }{ { m }^{ 2 }{ { v }_{ 0 }^{ 2 } } } } } \)

87.

Identify the mathematical expression for amplitude modulated wave:

(a)

\({ A }_{ c }sin\left[ { { \omega }_{ c }+{ k }_{ 1 }{ v }_{ m }\left( t) \right] t+\phi } \right] \)

(b)

\({ A }_{ c }sin\left[ { { \omega }_{ c }t+{ \phi +k }_{ 2 }{ v }_{ m }(t) } \right] \)

(c)

\([\{ { A }_{ c }+{ k }_{ 2 }{ v }_{ m }(t)\} sin\left( { \omega }_{ c }t+\phi \right) ]\)

(d)

\({ A }_{ c }{ v }_{ m }(t)sin\left( { \omega }_{ c }t+\phi \right) \)

88.

\(I-V\)characteristics of four devices are shown in Fig.

Identify devices that can be used for modulation:

(a)

'i' and 'iii'

(b)

only 'iii'

(c)

'ii' and some regions of 'iv'

(d)

All the devices can be used

89.

The Bohr model for the spectre of a H-atom

(a)

will not be applicable to hydrogen in the molecular form

(b)

will not be applicable as it is for a He-atom

(c)

is valid only at room temperature

(d)

predicts continuous as well as discrete spectral lines

90.

O₂ molecule consists of two oxygen atoms.In the molecule, nuclear force between the nuclei of the two atoms

(a)

is not important because nuclear forces are short-ranged

(b)

is as important as electrostatic force for binding the two atoms

(c)

cancels the repulsive electrostatic force between the nuclei

(d)

is not important because oxygen nucleus have equal number of neutrons and protons.

91.

A plane electromagnetic wave propagating along \(x\)direction can have the following Paris of E and B:

(a)

\({ E }_{ x }.B_{ Y }\)

(b)

\({ E }_{ y }.B_{ z }\)

(c)

\({ B }_{ x }.E_{ y }\)

(d)

\({ E }_{ x }.B_{ y }\)

Visit QB365-SLMS - https://www.qb365.in/slms/

Answers Key:

Multiple Choice Question

91 x 1 = 91

(b)
continuous if there is no charge at that point

(b)
4

(b)
k = 1

(b)
\(2\pi rB\left( \frac { dr }{ dt } \right) \)

(d)
\(\frac { \left( B\pi { r^{ 2 } }\omega \right) ^{ 2 } }{ 8R } \)

(b)
\(\vec { \upsilon } =\vec { E } \times \vec { B } /{ B }^{ 2 }\)

(d)
\(m{ E }^{ 2 }/2q{ B }^{ 2 }\)

10.

(d)
1

11.

(d)
their ability to conduct current

12.

(a)
17+9.625

13.

(b)
The driving force can given no energy to the oscillator (P = 0) in some cases

14.

15.

(b)
another capacitor should be added in parallel to the first

16.

(d)
\(10 \ \mu A\)

17.

(b)
60 db

18.

(b)
the coil moving in a time varying magnetic field

19.

(a)
a direct current is passing through the plate

20.

21.

(b)
the stopping potential will be 0.6 volt

22.

23.

(b)
50 cm

24.

25.

(a)
\(10^{ 17 }/m^{ 3 }\)

26.

(e)
\({ \lambda }_{ e },{ >\lambda }_{ p }>{ \lambda }_{ \alpha }\)

27.

28.

29.

(b)
3/8

30.

31.

(d)
Zero

32.

(d)
step up/step down transformer

33.

34.

(b)
actual transfer of electrons

35.

(d)
human body

36.

(d)
1.33 cm

37.

(b)
\({ \mu }_{ o }nI/2\)

38.

39.

(a)
decreases

40.

(b)
\(2 q\over \epsilon_o\)

41.

(b)
\(5\times { 10 }^{ 9 }cm\)

42.

(b)
\(2.4\times { 10 }^{ 20 }Hz\)

43.

44.

(a)
1.732

45.

(a)
electrons move from lower energy level to higher energy level in the condition band

46.

(b)
90^o

47.

48.

(d)
\({ V }_{ 1 }+\frac { h }{ e } ({ f }_{ 2 }-{ f }_{ 1 })\)

49.

(b)
2.14

50.

(d)
\(greater than \ v{ \left( \frac { 3 }{ 4 } \right) }^{ 1/2 }\)

51.

(b)
\({ K }_{ 1 }<\left( \frac { { K }_{ 2 } }{ 3 } \right) \)

52.

(a)
\(4\lambda \)

53.

(a)
\(6000 \ \overset { \circ }{ A } \)

54.

(d)
real or virtual depending on position of object

55.

(a)
\(-\frac { 1 }{ { m }^{ 2 } } \)

56.

(a)
The wavefront is spherical

57.

58.

(d)
3.4 eV

59.

(b)
150

60.

(a)
\(\frac { 1 }{ R } \sqrt { \frac { L }{ C } } \)

61.

(a)
it has no charge carriers

62.

(a)
electric field is zero

63.

(b)
273\({ m }_{ e }\)

64.

(a)
Optical fibre communication

65.

(a)
Ionosphere

66.

67.

68.

(a)
\(\oint { \overset { \rightarrow }{ E } .\overset { \rightarrow }{ ds } } =\frac { q }{ { \epsilon }_{ 0 } } \)

69.

Conductor

70.

(b)
\({ u }_{ E }{ +u }_{ m }\)

71.

(d)
not a single electron will be emitted.

72.

73.

74.

(b)
20 Hz to 20 kHz

75.

(a)
noise

76.

(d)
\({ v }_{ g }={ v }_{ x }={ v }_{ m }\)

77.

(b)
2.45 V/m

78.

(c)
\(\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ B } \ and \ \overset { \rightarrow }{ K } \parallel \overset { \rightarrow }{ E } \times \overset { \rightarrow }{ B } \)

79.