Series GEFH1/C SET~1

àíZ-nÌ H$moS>
amob Z§. Q.P. Code 55/C/1
Roll No.
narjmWu àíZ-nÌ H$moS> >H$mo CÎma-nwpñVH$m Ho$
_wI-n¥ð >na Adí` {bIo§ &
Candidates must write the Q.P. Code
on the title page of the answer-book. *

^m¡{VH$ {dkmZ (g¡ÕmpÝVH$)

PHYSICS (Theory)
:3 : 70
Time allowed : 3 hours Maximum Marks : 70
ZmoQ> / NOTE :
(i) H¥$n`m Om±M H$a b| {H$ Bg àíZ-nÌ _o§ _w{ÐV n¥ð>
27 h¢ &
Please check that this question paper contains 27 printed pages.
(ii) àíZ-nÌ _| Xm{hZo hmW H$s Amoa {XE JE àíZ-nÌ H$moS> H$mo narjmWu CÎma-nwpñVH$m Ho$ _wI-n¥ð> na
{bI| &
Q.P. Code given on the right hand side of the question paper should be written
on the title page of the answer-book by the candidate.
(iii) H¥$n`m Om±M H$a b| {H$ Bg àíZ-nÌ _| >35 àíZ h¢ &
Please check that this question paper contains 35 questions.
(iv) H¥$n`m àíZ H$m CÎma {bIZm ewê$ H$aZo go nhbo, CÎma-nwpñVH$m _| àíZ H$m H«$_m§H$ Adí`
{bI| &
Please write down the serial number of the question in the
answer-book before attempting it.
(v) Bg àíZ-nÌ 15 {_ZQ >H$m g_` {X`m J`m h¡ & àíZ-
10.15 ~Oo {H$`m OmEJm & 10.15 ~Oo go 10.30 ~Oo VH$ N>mÌ Ho$db àíZ-
Ad{Y Ho$ Xm¡amZ do CÎma-nwpñVH$m na H$moB© CÎma Zht {bI|Jo &
15 minute time has been allotted to read this question paper. The question
paper will be distributed at 10.15 a.m. From 10.15 a.m. to 10.30 a.m., the
students will read the question paper only and will not write any answer on the
answer-book during this period.

55/C/1 ^ Page 1 of 27 P.T.O.

General Instructions :
Read the following instructions very carefully and strictly follow them :
(i) This question paper contains 35 questions. All questions are compulsory.
(ii) This question paper is divided into five Sections A, B, C, D and E.
(iii) In Section A Questions no. 1 to 18 are Multiple Choice (MCQ) type
questions, carrying 1 mark each.
(iv) In Section B Questions no. 19 to 25 are Very Short Answer (VSA) type
questions, carrying 2 marks each.
(v) In Section C Questions no. 26 to 30 are Short Answer (SA) type questions,
carrying 3 marks each.
(vi) In Section D Questions no. 31 to 33 are Long Answer (LA) type questions
carrying 5 marks each.
(vii) In Section E Questions no. 34 and 35 are case-based questions carrying
4 marks each.
(viii) There is no overall choice. However, an internal choice has been provided in
2 questions in Section B, 2 questions in Section C, 3 questions in Section D and
2 questions in Section E.
(ix) Use of calculators is not allowed.
Use the following values of physical constants, if required :
c=3 108 m/s

h = 6.63 10 34 Js

e = 1.6 10 19 C

0 =4 10 7 T m A 1

0 = 8.854 10 12 C2 N 1 m 2
1
=9 109 N m2 C 2
4
0

Mass of electron (me) = 9.1 10 31 kg

Mass of neutron = 1.675 10 27 kg

Mass of proton = 1.673 10 27 kg

6.023 1023 per gram mole

Boltzmann constant = 1.38 10 23 JK 1

55/C/1 Page 3 of 27 P.T.O.

 SECTION A
1. A small object lies at the bottom of a vessel filled with water (refractive
index 4/3) up to a height H. When viewed from a point above the surface
of water, the object appears raised by n percent of H. The value of n is :
(a) 15 (b) 20
(c) 25 (d) 33
^ ^
2. An electron with velocity v = (vx i + vy j ) moves through a magnetic
^ ^
field B = (Bx i By j ). The force F on the electron is : (e is the
magnitude of its charge)
^ ^
(a) e (vx By vy Bx) k (b) e (vx By vy Bx) k
^ ^
(c) e (vx By + vy Bx) k (d) e (vx By + vy Bx) k

3. A bar magnet is cut into two equal halves parallel to its magnetic axis.
The physical quantity that remains unchanged is :
(a) pole strength (b) magnitude of magnetisation
(c) moment of inertia (d) magnetic moment

4. In a series LC circuit connected to an ac source, with the increase in the

frequency of the source, the net reactance :
(a) increases linearly
(b) decreases linearly
(c) first increases to become maximum and then decreases to zero
(d) first decreases to become zero and then increases

5. Which of the following physical quantities remain the same for X-ray, red
light and radio waves when travelling through a medium ?
(a) Wavelength (b) Speed
(c) Frequency (d) Momentum

6. uble-slit experiment, the intensity on the screen is I 0 at a

point where path difference is . The intensity at the point where path
difference is is :
4
I0 I0
(a) (b)
4 2
(c) I0 (d) zero

55/C/1 Page 5 of 27 P.T.O.

7.
momentum with the de Broglie wavelength associated with it ?

8. In the nuclear reaction 7 N14 2

He4 X 1
H1 , X represents :

(a) 7
O16 (b) 8
N17

(c) 8
O17 (d) 7
N16

9. The given figure shows a capacitor C and a resistor R connected in series

to an ac source. V1 and V2 are voltmeters and A is an ammeter.

Which of the following statements is correct ?

(a) Current in the circuit lags in phase with voltage shown in V2 .
(b) The voltage shown in V1 is ahead in phase with voltage shown in V2.
(c) The current in the circuit and the voltage shown in V1 are always
in phase.
(d) The voltage shown in V1 lags behind in phase with the voltage
shown in V2 .

55/C/1 Page 7 of 27 P.T.O.

10. Light of frequency 1·5 v0 is incident on a photosensitive material of
threshold frequency v0. If the frequency of the incident radiation is kept
constant and intensity is increased, the photo current will :
(a) increase
(b) decrease
(c) not change
(d) first decrease and then become zero

11. The impact parameter for an alpha particle approaching a target nucleus
is maximum when the scattering angle ( ) is :
(a) 0 (b) 90
(c) 180 (d) 45

12. Two nuclei have their mass numbers in the ratio of 1 : 27. What is the
ratio of their nuclear densities ?
(a) 1 : 27 (b) 1:1
(c) 1:9 (d) 1:3

13. A plane wave is incident on a concave mirror of radius of curvature R.

The reflected wave is a spherical wave of radius :
R R
(a) (b)
4 2
(c) R (d) 2R

14. A planar loop is rotated in a magnetic field about an axis perpendicular

to the field. The polarity of induced emf changes once in each :
1
(a) 1 revolution (b) revolution
2

1 3
(c) revolution (d) revolution
4 4
55/C/1 Page 9 of 27 P.T.O.
15.
to provide smooth output of a half-wave rectifier ?

Questions number 16 to 18 are Assertion (A) and Reason (R) type questions. Two
statements are given one labelled Assertion (A) and the other labelled Reason
(R). Select the correct answer from the codes (a), (b), (c) and (d) as given below.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the
correct explanation of the Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not
the correct explanation of the Assertion (A).
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false and Reason (R) is also false.

16. Assertion (A) : The temperature coefficient of resistance is positive for

metals and negative for semi-conductors.
Reason (R) : The charge carriers in metals are negatively charged
whereas in semiconductors they are positively charged.

17. Assertion (A) : A planar loop of irregular shape carrying current is

subjected to a magnetic field acting perpendicular to the
plane of the loop. If the wire is flexible, the loop takes a
circular shape.
Reason (R) : The force acting on each point of a current carrying loop,
in a magnetic field perpendicular to its plane, is radially
outward.
55/C/1 Page 11 of 27 P.T.O.
18. Assertion (A) : Silicon is preferred over germanium for making
semiconductor devices.
Reason (R) : The energy gap for germanium is more than the energy
gap for silicon.
SECTION B
19. (a) The electric field of an electromagnetic wave passing through
vacuum is represented as Ex = E0 sin (kz t). Identify the
parameter which is related to the (i) wavelength, and (ii) the
frequency of the wave in the above equation.
(b) Write two properties of a medium that determine the velocity of
light in that medium. 2

20. Two identical bars, one of a paramagnetic material and another of a

diamagnetic material are kept in a uniform magnetic field. Show
diagrammatically the modifications in the pattern of magnetic field in
each case. How are the two materials affected by increase in
temperature ? 2

21. Light of wavelength 3500 Å is incident on two metals A and B. Which of

them will yield photoelectrons, if their work functions are 4 2 eV and
1 9 eV respectively ? Make the necessary calculations to justify your
answer. 2

22. The inward and the outward electric flux through a Gaussian surface are
2 and respectively.
(a) What is the net charge enclosed by the surface ?
(b) If the net outward flux through the surface were zero, can it be
concluded that there were no charges inside the surface ? Justify
your answer. 2

23. (a) 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 the
glow becomes steady ? Why ? 2
OR
(b) A battery is connected first across the series combination and then
across the parallel combination, of three resistances R, 2R and 3R.
In which of the three resistances will power dissipated be maximum
in the two cases ? Justify your answer. 2
55/C/1 Page 13 of 27 P.T.O.
24. The figure shows the variation of stopping potential V0 with frequencies
of incident monochromatic beam for a metal. Such a graph was first
obtained by R.A. Millikan in 1916 for sodium.

metal, given the value of charge on electron. 2

25. (a) A uniform electric field E of 500 N/C is directed along +x axis.
O, B and A are three points in the field having x and y coordinates
(in cm ) (0, 0), (4, 0) and (0, 3) respectively. Calculate the potential
difference between the points (i) O and A, and (ii) O and B. 2
OR
(b) Three point charges 1 C, 1 C and 2 C are kept at the vertices
A, B and C respectively of an equilateral triangle of side 1 m. A1,
B1 and C1 are the midpoints of the sides AB, BC and CA
respectively. Calculate the net amount of work done in displacing
the charge from A to A1, from B to B1 and from C to C1. 2

SECTION C
26. (a)
when a rectangular conducting loop abcd in xy-plane is moved into
a region of magnetic field which is directed along z-axis. 3

OR
55/C/1 Page 15 of 27 P.T.O.
 (b) Two identical circular loops, one of copper and the other of
aluminium are rotated about their diameters with the same
angular speed in a magnetic field directed perpendicular to their
axes of rotation. Compare (i) the emf induced, and (ii) the current in
the two loops. Justify your answers. 3

27. (a) It is not advisable to use a galvanometer as such to measure

current directly. Why ?

(b) Why should the value of resistance connected in parallel to a

galvanometer be low ?

(c) Is the reading shown by an ammeter in a circuit less than or more

than the actual value of current flowing in the circuit ? Why ? 3

28. The figure shows a capacitor C, a variable resistor R and a bulb

connected in series to the ac source of frequency (v). The bulb glows with
some brightness.

How will the glow of the bulb be affected, if the

(a) separation between the plates of the capacitor is doubled, keeping

resistance R and frequency (v) the same ?

(b) resistance R is decreased keeping the value of capacitance C and

frequency (v) same ?

(c) frequency of ac source is decreased for the same value of C and R ?

Justify your answer in each case. 3

55/C/1 Page 17 of 27 P.T.O.

29. (a) (i) In which case is diffraction effect more dominant slit
formed by 2 blades or slit formed by two fingers ?
(ii) Yellow light ( = 6000 Å) illuminates a single slit of width
1 10 4 m. Calculate (i) the distance between two dark lines
on either side of central maximum, in the diffraction pattern
observed on a screen kept 1·5 m away from the slit, and (ii) the
angular spread of the first minimum. 3
OR
(b) (i) What will be the colour of the central bright fringe in Y
double slit experiment if the monochromatic source is replaced
by a source of white light ? Give reason for your answer.
(ii)
0 3 mm and the screen is placed 1 5 m away from the slits.
The distance between the central bright fringe and the sixth
bright fringe is found to be 1 8 cm. Find the wavelength of
light used in the experiment. 3

30. (a) (i) An electron in a hydrogen atom jumps from second excited
state to the first excited state. Name the spectral series in the
spectrum of hydrogen atom to which the emitted radiation
belongs.
(ii)

of Hydrogen spectrum. 3
OR
(b) (i) An -particle having kinetic energy K approaches a nucleus of
atomic number Z. It gets close to the nucleus and then
approaches a distance (d) and reverses its direction. Obtain an
expression for the distance of closest approach (d) in terms of
kinetic energy of the -particle.

(ii) A proton and an alpha particle approach a target nucleus in

head-on position, with equal velocities. Find the ratio of their
distances of closest approach to the target nucleus. 3

55/C/1 Page 19 of 27 P.T.O.

 SECTION D

31. (a) (i) Draw a labelled ray diagram of an astronomical telescope to

show the image formation of a distant object by it in normal
adjustment. What are the main considerations required in
selecting the objective and eyepiece lenses so that the
telescope has large magnifying power and high resolution ?

(ii) A biconvex lens of focal length 20 cm is immersed in water,

4
whose refractive index is . Find the change, if any, in the
3
nature and the focal length of the lens. Refractive index of the
3
material of convex lens is . 5
2
OR
(b) (i) Draw a ray diagram showing refraction of light through a
prism of angle A and obtain the relation between , A and the
angle of minimum deviation m.

(ii) An equiconvex lens of radius of curvature R and made of glass

of refractive index is cut into two identical plano-convex
lenses. Find the focal length of the plano-convex lenses. 5

32. (a) (i) Derive the relation between the current and the drift velocity
of free electrons in a conductor. Briefly explain the variation
of resistance of a conductor with rise in temperature.
(ii) An ammeter, together with an unknown resistance in series is
connected across two identical batteries, each of emf 1 5 V,
connected (i) in series, and (ii) in parallel. If the current
1 1
recorded in the two cases be A and A respectively,
2 3
calculate the internal resistance of each battery. 5

OR

55/C/1 Page 21 of 27 P.T.O.

 (b) (i) State Kirchhoff
balance for a Wheatstone Bridge.

(ii) Use Kirchhoff

through the branches MN, TO and SP in the circuit shown in
the figure. 5

33. (a) (i) Draw the circuit diagram used to study I V characteristics of
a p-n junction diode in conducting mode. Mark on the graph
the threshold voltage of the diode. Explain the significance of
this voltage.
(ii) In the circuit shown in the figure, the forward voltage drop
across the diode is 0 3 V. Find the voltage difference between
A and B. 5

OR
(b) (i) Briefly describe the classification of solids into metals,
insulators and semi-conductors on the basis of energy level
diagrams.

(ii) In a silicon diode, the current increases from 10 mA to 20 mA

when the voltage changes from 0 6 V to 0 7 V. Calculate the
dynamic resistance of the diode. 5
55/C/1 Page 23 of 27 P.T.O.
 SECTION E

34.

A parallel plate capacitor is an arrangement of two identical metal plates

kept parallel, a small distance apart. The capacitance of a capacitor
depends on the size and separation of the two plates and also on the
dielectric constant of the medium between the plates. Like resistors,
capacitors can also be arranged in series or parallel or a combination of
both. By virtue of electric field between the plates, charged capacitors
store energy.

(a) The capacitance of a parallel plate capacitor increases from 10 F to

80 F on introducing a dielectric medium between the plates. Find
the dielectric constant of the medium. 1

(b) n capacitors, each of capacitance C, are connected in series. Find

the equivalent capacitance of the combination. 1

(c) A capacitor is charged to a potential (V) by connecting it to a

battery. After some time, the battery is disconnected and a
dielectric is introduced between the plates. How will the potential
difference between the plates, and the energy stored in it be
affected ? Justify your answer. 2

OR
55/C/1 Page 25 of 27 P.T.O.
 (c) Find the equivalent capacitance between points A and B, if
capacitance of each capacitor is C. 2

35. A prism is a solid transparent medium bounded by three rectangular

faces with a triangular base and a top. A ray of light incident at angle i
on one face of a prism suffers two refractions on passing through a prism.
Hence it deviates through a certain angle from its original path. The
angle of deviation becomes minimum ( = m) for a certain value of angle
i. In such a condition, the refracted ray inside the prism becomes parallel
to its base. An expression for refractive index of the material of the
prism can be obtained in terms of angle A and angle m.

(a) Show in a figure the variation of angle with angle of incidence i. 1

(b) Show that for a prism of small angle A, the refractive index of its
material can be written as =1+ m . 1
A
(c) A ray of light passes through an equilateral prism such that both
the angle of incidence and the angle of emergence are equal to the
angle of prism A. Find the refractive index of the material of the
prism, in terms of A. 2
OR
(c) A ray of light passes through a prism of angle 75 , as shown in the
figure. The refractive index of the material of the prism, with
respect to its surrounding is 2 . Find the angle of incidence i. 2

55/C/1 Page 27 of 27 P.T.O.