When two capacitors charged to different potentials are connected by a conducting wire, what is not true?

1

(a)

charge lost by one is equal to charge gained by the other

(b)

potential lost by one is equal to potential gained by the other

(c)

some energy is lost

(d)

both the capacitor acquire a common potential

Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region

1

(a)

the electric field is necessarily zero

(b)

the electric field is due to the dipole moment of the charge distribution only

(c)

the dominant electric field is  \(\alpha {1\over r^3}\) , for large r , where r is the distance from a origin in this region.

(d)

the work done to move a charged particle along a closed path, away from the region, will be zero.

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,

1

(a)

the declination varies between \(11.3°\)W to \(11.3°\)

(b)

the least declination is \(\ 0°\)

(c)

the plane defined by dipole axis and earth axis passes through Greenwich.

(d)

declination averaged over the earth must be always negative.

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

1

(a)

q/2 m

(b)

q/m

(c)

2 q/m

(d)

\(q/\pi \ m.\)

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 :

1

(a)

\(\frac { { \phi }_{ 2 }-{ \phi }_{ 1 } }{ 5Rnt } \)

(b)

\(\frac { -n\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ 5Rt } \)

(c)

\(\frac { -\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ Rnt } \)

(d)

\(\frac { -n\left( { \phi }_{ 2 }-{ \phi }_{ 1 } \right) }{ Rt } \)

An electromagnetic wave going through vacuum is denoted by \(E={ E }_{ 0 } \ sin \ (kz-\omega t)\). Which of the following is/are independent of wavelength?

1

(a)

k

(b)

\(\omega \)

(c)

\(k/\omega \)

(d)

\(k\omega \)

Sound waves are not electromagnetic waves as 

1

(a)

they cannot undergo interference

(b)

they cannot undergo diffraction

(c)

they cannot be polarized

(d)

they cannot pass through vacuum

Photoelectric effect supports the quantum nature of light because

1

(a)

there is minimum frequency of light below which no photoelectrons are emitted

(b)

the maximum K.E. of photoelectrons emitted depends only on the frequency of the incident light and on its intensity

(c)

even when metal surface is faintly illuminated, the photoelectrons leave the surface immediately

(d)

electric charge of photoelectron is quantised

For a radioactive material, its activity A and rate of change of its activity R are defined as
\(A=-\frac { dN }{ dt } \quad and\quad R=-\frac { dA }{ dt } ,\)
where N (t) is the number of nuclei at time t. Two radioactive sources P (mean life \(\tau \)) and Q (mean life \(2\tau \)) have the same activity at t = 0. Their rates of change of activities at t = \(2\tau \) are \({ R }_{ P } \ and \ { R }_{ Q },\) respectively. If \(\frac { { R }_{ P } }{ { R }_{ Q } } =\frac { n }{ e } ,\) then the value of n is

1

(a)

1

(b)

2

(c)

3

(d)

4

If the ratio of the concentration of electrons and of holes in a semiconductor is 7/5 and the ratio of currents is 7/4 then what is the ratio of their drift velocities?

1

(a)

4/7

(b)

5/8

(c)

4/5

(d)

 5/4

The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens' is 15 ern, then the nature and focal length of the other lens would be

1

(a)

convex, 9 cm

(b)

concave, 9 cm

(c)

convex, 25 cm

(d)

concave, 25 cm

Write two applications of capacitors in electrical circuits?

1

(a)

(i) Capacitors are used in radio circuits for tuning purposes.
(ii) Capacitors are used in power supplies for smoothing the rectified current.

Electrons are transferred from the material whose ............. is ....... to the material whose ............ is ...............

1

(a)

work function; lower, work function ; higher

In an experiment on meter bridge, if the balancing length AC is 'x' what would be its value when the radius of the meter bridge wire AB is doubled? Justify your answer.

1

(a)

When cells are connected in parallel, what will be the effect on
(i) current capacity
(ii) e.m.f  of the cells.

1

(a)

(i) Current capacity from the combination of cells is the total current available from the cell. Current capacity increases for the parallel combination of cells.
(ii) The effect e.m.f. of the cells of equal e.m.f. in parallel will be equal to e.m.f. of one cell.

A copper wire is bent into a square of each side 6cm.If a current of 2A is passed through a wire what is the magnetic field at the centre of the square?

1

(a)

B1 = 4 x \({ \mu }_{ 0 }\) I/4\(\pi\) a/2 (sin 45  + sin 45)
= 4 x \({ \mu }_{ 0 }\)  2/4 \(\Pi \) x 3  (1 / 1.414  + 1/414 )
= 2\({ \mu }_{ 0 }\)/3\(\Pi \)  (1/.414 ) + 1/414 ) T

In hydroelectric power station, ....................of falling water is converted into................. .

1

(a)

kinetic energy; electrical energy

Arrange the following in decending order of wavelength:

X-rays, Radiowave, Blue light, infrared light.

1

(a)

1. Resolving power of an optical instrument is the ability of the instrument to ___________ or ____________ the images of ____________.

   1

   (a)

   resolve; see as separate; two closely spaced objects.

2. Do all the electrons that absorb a photon come out as photoelectrons?

   1

   (a)

   In photoelectric effect,. we can observe that most electrons get scattered into the metal by absorbing a photon.
   Thus, all the electrons that absorb a photon does not come out as photoelectron. Only a few comes out of metal whose energy becomes greater than the work functibn of metal.

1. How does the dc current gain of a transistor change, if the width of the base region is increased?

   1

   (a)

2. Give one example of point-to-point communication mode. (Any one)

   1

   (a)

   Telephone call; Microwave relay

Deduce the expression for the electric field E due to a system of two charges q₁ and q₂ with position vectors r₁ and r₂ at a point r with respect to common origin.

2

(a)

Under what condition is the heat produced in an electric circuit:
(i) directly proportional
(ii) inversely proportional to the resistance of the circuit?

2

(a)

Define magnetic susceptibility of a material. Name two elements one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

2

(a)

Define root mean square or virtual or effective value of a.c.

2

(a)

Draw a labelled diagram of Hertz's experiment set upto produce electromagnetic waves. Explain the generation of electromagnetic waves using this set up.

2

(a)

1. Why is the amplitude of modulating signal kept less than the amplitude of carrier wave?

   2

   (a)

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.

   2

   (a)

1. 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

   2

   (a)

A 800 pF capacitor is charged by a 100 V battery. Ater sometime, the battery is disconnected. The capacitor. What is the electrostatic energy stored?

3

(a)

A long straight wire carrying current of 25 A rests on a table as shown in the figure.  Another wire PQ of length 1m, mass 2.5 g carries the same current but in the opposite direction.  The wire PQ is free to slide up and down.  To what height will PQ rise?

3

(a)

Over a solenoid of 50cm length and 2cm radius having 500 turns, is wound another wire of 50 turns near the centre. Calculate mutual inductance of the two coils. If current in primary changes from 0 to 5 in 0.02 s, what is the emf induced in secondary coil?

3

(a)

A parallel plate capacitor has circular plates, each of radius 8 cm. It is being charged so that the electric field between the gap of two plates rises steadily at the rate of \({ 10 }^{ 13 }\quad V{ m }^{ -1 }{ s }^{ -1 }\) find the value of displacement current.

3

(a)

How would you set up a circuit to obtain NOT gate using a transistor?

3

(a)

A radio set can be turned to any station in the frequency range 6 MHz to 12 MHz band.What is the corresponding wavelength band of radio set?

3

(a)

An object is placed at (i) 10 cm, (ii) 5 cm in front of a concave mirror of radius of curvature 15 cm. Find the position, nature, and magnification of the image in each case.

3

(a)

(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 R_2.. 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.

3

(a)

Bala and rama (Class X students), were assigned a project based on magnetism.In their project work, they had calculated the value of the earth's magnetic field.When they submitted their project for verification.Mr.Santosh, their Physics techer, corrected the mistakes. He also suggested few books which could be useful for them.
i) What values did Mr.Santosh exhibit towards his students? Mention any two.
ii) Mention the three magnetic elements required to calculate the value of the earth's magnetic field.
iii) What is the strength of the earth's magnetic fields at the surface of the earth?

5

(a)

(a) Explain nuclear fusion. What are the conditions for fusion?

(b) What are the sources of energy in sun and stars ?

5

(a)

What should be the distance between the object in Exercise and the magnifying glass if the virtual image of each square in the figure is to have an area of 6.25 mm² . Would you be able to see the squares distinctly with your eyes very close to the magnifier?

5

(a)

Two parallel plate air capacitors have their plate areas 100 and 500cm² respectively. If they have the same charge and potential and the distance between the plates of the first capacitor is 0.5mm, what is the distance between the plates of second capacitor?

5

(a)

A series LCR circuit is connected to an a.c. source (200V, 50Hz). The voltages across resistor capacitor and inductor are respectively 200V, 250V and 250V. The algebraic sum of the voltages across the three elements is greater than the source voltage. Why?
If R = 40\(\Omega \), calculate current in the circuit.

5

(a)

Find the de-Broglie wavelength(in \(\overset { \circ }{ A } \) ) associated with an example with an electron moving with a velocity 0.6c, where c=\(3\times { 10 }^{ 8 }m/s\)and rest mass of electron=\(9.1\times { 10 }^{ -31 }kg\), \(h=6.6\times { 10 }^{ -34 }Js\)

5

(a)