Practice Test Paper 2
Physics
(Theory) – XII
Time
allowed: 3 hours Maximum
marks: 70
Q. 1.

An
electron beam projected along +Xaxis, experiences a force due to a magnetic
field along the +Yaxis. What is the direction of the magnetic field?

1

Q. 2.

Name
an appropriate communication channel needed to send a signal of bandwidth
100 kHz over a distance of 8 km.

1

Q. 3.

Ultraviolet
light is incident on two photosensitive materials having work functions W_{1}
and W_{2} (W_{1}>W_{2}). In which case will the
kinetic energy of the emitted electrons be greater? Why?

1

Q. 4.

Name
the device which can represent digital data by analog signals and viceversa.

1

Q. 5.

Why is
the conductivity of ntype semiconductor greater than that of the ptype
semiconductor even when both of these have same level of doping?

1

Q. 6.

Define the terms ‘Magnetic Dip’ and ‘Magnetic Declination’
with the help of relevant diagrams.

2

Q. 7.

A 4mF
capacitor is charged by a 200 V supply. The supply is then disconnected and
the charged capacitor is connected to another uncharged 2 mF
capacitor. How much electrostatic energy of the first capacitor is lost in
the process of attaining the steady situation?

2

Q. 8.

State
the underlying principle of an a.c. generator. Write the relationship between
the peak value and r.m.s. value of alternating voltage.

2

Q. 9.

A
voltage of 30 V is applied across a carbon resistor with first, second and
third rings of blue, black and yellow colours respectively. Find the value of
current through the resistor.

2

Q. 10.

Define
the term threshold frequency and work function in relation to photoelectric
effect.

2

Q. 11.

Explain,
with the help of a circuit diagram, the use of npn transistor as an
amplifier in common emitter configuration.

2

Q. 12.

Write
the expression for frequency of an ideal LC circuit. In an actual circuit,
why do the oscillations ultimately die away?

2

Q. 13.

State
Gauss’s theorem. Apply this theorem to obtain the expression for the electric
field intensity at a point due to an infinitely long, thin, uniformly charged
straight wire.

3

Q. 14.

State
the principle of potentiometer. Draw a circuit diagram used to compare the
e.m.f. of two primary cells. Write the formula used. How can the sensitivity
of a potentiometer be increased?

3

Q. 15.

Define
selfinductance and give its S.I. unit. Derive an expression for
selfinductance of a long, aircored solenoid of length l, radius r, and
having N number of turns.

3

Q. 16.

State
BiotSavart law. Apply it to calculate the magnetic field at a point near a
current carrying long straight wire.

3

Q. 17.

Sate
the principle of potentiometer. With the help of circuit diagram, describe a
method to find the internal resistance of a primary cell.

3

Q. 18.

Explain the following terms:
(a)
Ground waves
(b)
Space waves
(c)
Sky waves

3

Q. 19.

Calculate
the binding energy per nucleon (in MeV) of the nucleus . Given mass of = 1.00783 u, mass of = 1.00867 u, mass of
= 55.934939 u, 1u =
931 MeV/c^{2}.

3

Q. 20.

What
do the acronyms ‘LASER’ and ‘LED’ stand for? Name the factor which
determines:
(a) Frequency, and
(b) Intensity of light emitted by LED.

3

Q. 21.

What are coherent sources? How
does the width of interference fringes in Young’s double slit experiment
change when
(a)
The distance between the slits and screen is
decreased?
(b)
The frequency of the source is increased?
Justify your answer in each case.

3

Q. 22.

Distinguish between analog and digital communication.
Write any two modulation techniques employed for the digital data. Describe
briefly any one of the techniques used.

3

Q. 23.

On the
basis of energy band diagrams distinguish between metals, insulators and
semiconductors

3

Q. 24.

(a)
Show that the decay rate ‘R’ of a sample of a
radionuclide is related to the number of radioactive nuclei ‘N’ at the same
instant by the expression R = lN.
(b)
The halflife of against adecay is 1.5x1017s. What is the activity of a sample
of having 25x1020
atoms?

3

Q. 25.

(a)
With the help of a schematic sketch of a cyclotron
explain its working principle. Mention its two applications. What is the
important limitation encountered in accelerating a light elementary particle
such as electron to high energies?
(b)
A particle of mass m and charge q moves at right angles
to a uniform magnetic field. Plot a graph showing the variation of the radius
of the circular path described by it with the increase in its (i) charge,
(ii) kinetic energy, where, in each case other factors remain constant.
Justify your answer.
Or
(a)
Using BiotSavart law derive an expression of the
magnetic field due to a current carrying loop at a point along the axis of
the loop.
(b)
A long straight conductor carries a steady current
‘I’. The current is uniformly distributed across its crosssection of radius
‘a’. Plot a graph showing the variation of the magnetic field ‘B’ produced by
the conductor with distance ‘r’ from the axis of the conductor in the region
(i) r<a, and (ii) r>a.

5

Q. 26.

Show by a diagram the image formation of a point object by a thin
double convex lens having radii of curvature R_{1} and R_{2}.
Hence derive the formula
where f is the focal length and n is refractive index of
material of the lens.
Or
State
Huygen’s principle. Use Huygen’s construction to explain refraction of a plane
wavefront at a plane surface. Draw diagrams to show the behaviour of a (a)
convex lens, (b) concave mirror when a plane wavefront falls on it.

5

Q. 27.

With the help of a neat and labelled diagram, explain
the principle, construction and working of an a.c. generator.
Or
Explain, with the help of a neat and labelled diagram, the
principle, construction and working of a transformer.

5
