Practice Test Paper 3
Physics
(Theory) – XII
Time
allowed: 3 hours Maximum
marks: 70
Q. 1.

An
electron and a proton, moving parallel to each other in the same direction
with equal momenta, enter into a uniform magnetic field which is at right
angles to their velocities. Trace their trajectories in the magnetic
field.

1


Q. 2.

Two
identical loops, one of copper and another of constantan are removed from a
magnetic field within the same time interval. In which loop will the induced
current be greater?

1


Q. 3.

The
power factor of an a.c. circuit is 0.5. What will be the phase difference
between voltage and current in this circuit?

1


Q. 4.

Does
the ‘stopping potential’ in photoelectric emission depend upon
(a) the
intensity of the incident radiation in a photocell?
(b) The
frequency of the incident radiation?

1


Q. 5.

What
is the function of ‘cladding’ in a typical optical fibre?

1


Q. 6.

(a)
Draw the graphs showing variation of inductive
reactance and capacitive reactance with frequency of applied a.c. source.
(b)
Can the voltage drop across the inductor or the
capacitor in a series LCR circuit be greater than the applied voltage of the
a.c. source? Justify your answer.

2


Q. 7.

Define
electric field intensity. Write its S.I. unit. Write the magnitude and
direction of electric field intensity due to an electric dipole of length 2a
at the midpoint of the line joining the two charges.

2


Q. 8.

State
the underlying principle of a transformer. Write two causes of power loss in
it.

2


Q. 9.

Two dielectric slabs of dielectric constant K_{1}
and K_{2} are filled in between the two plates, each of area A, of
the parallel plate capacitor as shown in the figure. Find the net capacitance
of the capacitor.

2


Q. 10.

Explain
the term remote sensing in communication. Name the satellite used for this
purpose.

2


Q. 11.

With
the help of diagrams distinguish between forward biasing and reverse biasing
of a pn junction diode.

2


Q. 12.

Monochromatic
light is refracted from air into glass of refractive index n. Find the ratio
of wavelengths of the incident and refracted light.

2


Q. 13.

An
electric dipole is held in a uniform electric field. (a) using suitable
diagram, show that it does not undergo any translatory motion, and (b) derive
an expression for the torque acting on it and specify its direction.

3


Q. 14.

Explain,
with the help of diagram, the principle and working of an a.c. generator.
Write the expression for the e.m.f. generated in the coil in terms of its
speed of rotation.

3


Q. 15.

Define
the term ‘temperature coefficient of resistivity’. Write its SI unit. Plot a
graph showing the variation of resistivity of copper with temperature.

3


Q. 16.

Draw a
labelled diagram of a moving coil galvanometer. Explain its working
principle. Can this galvanometer be used to detect an a.c. in a circuit? Give
reason.

3


Q. 17.

A battery of emf 10 V and internal resistance 3Ω is
connected to a resistor R.
(a) If
the current in the circuit is 0.5 A, calculate the value of R.
(b) What
is the terminal voltage of the battery when the circuit is closed?

3


Q. 18.

Draw a labelled diagram of
experimental setup of Rutherford’s alpha particle scattering experiment.
Write two important inferences drawn from this experiment.

3


Q. 19.

With
the help of a labeled diagram explain in brief the working of a
cyclotron.

3


Q. 20.

Calculate
the binding energy per nucleon (in MeV) for and . Comment on the difference of these binding energies and
its significance in relation to adecay of the nuclei. Given: mass of = 1.00783 u, mass of = 1.00867 u, mass of
= 3.01664 u, mass of = 4.00387 u.

3


Q. 21.

A ground receiver station is receiving a signal at (a) 5
MHz and (b) 100 MHz, transmitted from a ground transmitter at a height of 300
m located at a distance of 100 km. Identify whether it is coming via space
wave or sky wave propagation or satellite transponder. (Given the value of
radius of the earth is 6400 km and maximum electron density, N_{max}
= 10^{12} m^{3})

3


Q. 22.

(a)
Draw the energy level diagram showing the emission of
bparticles
followed by grays
by a .
(b)
Plot the distribution of kinetic energy of bparticles
and state why the energy spectrum is continuous.

3


Q. 23.

Name the constituent radiation of electromagnetic spectrum
which
(a) is
used in satellite communication.
(b) is
used for studying crystal structure.
(c) is
similar to the radiations emitted during decay of radioactive nuclei.
(d) has
its wavelength range between 390 nm and 770 nm.
(e) is
absorbed from sunlight by ozone layer.
(f) produces
intense heating effect.

3


Q. 24.

Explain, with the help of a circuit diagram, how the
thickness of depleteion layer in a pn junction diode changes when it is
forward biased. In the following circuits which one of the two diodes is
forward biased and which is reverse biased?
10V
(a)
(b)
10
V

3


Q. 25.

Draw a level diagram of a Van de Graaff generator. Give
its principle and explain its working.
Or
Define
capacitance of a capacitor. Give its S.I. unit. Prove that the total
electrostatic energy stored in a parallel plate capacitor is CV^{2} and hence find the expression for the energy
density of the capacitor.

5


Q. 26.

(a)
Define the term ‘impedance of series LCR circuit’.
Derive a mathematical expression for it using Phasor diagram.
(b)
Obtain the resonant frequency of a series LCR circuit
with L = 2.0 H, C = 32 mF and R = 10 Ω
Or
(a) Distinguish
between the terms resistance, reactance and impedance of an a.c. circuit.
(b) A
100 mF
capacitor in series with a 40 Ω resistance is connected to a 100 V, 60 Hz
supply. Calculate (i) the reactance, (ii) impedance, and (iii) maximum
current in the circuit.

5


Q. 27.

Using Huygen’s principle, draw a diagram to show
propagation of a wavefront originating from a monochromatic point source.
Describe diffraction of light due to a single slit.
Explain formation of a pattern of fringes obtained on the screen and plot
showing variation of intensity with angle q in single slit
diffraction.
Or
What is meant by a linearly
polarized light? Which type of waves can be polarized? Briefly explain a
method for producing polarized light.
Two polaroids are placed at 90^{o} to each other
and the intensity of transmitted light is zero. What will be the intensity of
transmitted light when one more polaroid is placed between these two
bisecting the angle between them? Take intensity of unpolarised light as I.

5
