KVS ZONAL INSTITUTE OF EDUCATION AND TRAINING CHANDIGARH

PRE-BOARD PRACTICE PAPER PHYSICS XII (042)

2023-24 SUMMER KV
Maximum Marks: 70 Time Allowed: 3 hours.

General Instructions:

(1) There are 33 questions in all. All questions are compulsory.

(2) This question paper has 5 sections: Section A, Section B, Section
C, Section D Section E
(3) All the sections are compulsory.
(4) Section A contains 16 questions, 12 MCQ, and 04 Assertion
Reasoning based on 1 mark each,
(5) Section B contains 5 questions of two marks each,
(6) Section C contains 7 questions of three marks each,
(7) Section D contains 2 case study-based questions of four marks each
and
(8) Section E contains 3 long answer questions of five marks each.
(9) There is no overall choice. However, an internal choice has been
provided in one question in Section B, one question in Section C,
one question in each CBQ in Section D, and all three questions in
Section E.
You have to attempt only one of the choices in such questions.
(10) Use of calculators is not allowed.
(11) You may use the following values of physical constants where ever
necessary
i. c = 3 x 108 m/s
ii. me = 9.1 x10-31 kg
iii. h = 6.63 x10-34 Js
-
iv. ∈𝑜 = 8.854 x10 12 𝐶 2 𝑁 −1 𝑚−2
v. Avogadro’s number = 6.023 X 1023 per gram mole
vi. µo = 4π x 10-7 Tm𝐴−1
vii. e = 1.6 x 10-19 C
Q. SECTION – A M
NO.
1 Electric field intensity at a point in between two parallel sheets with like 1
charges of the same surface charge densities (σ) is
(a) σ/2ε0 (b) 3σ/ε0 (c) 2σ/ε0 (d) Zero
2 An electric dipole of dipole moment 4 x 10-5 Cm, kept in a uniform electric 1
field of 10-3 NC-1, experiences a torque of 2 x10-8 Nm. The angle which the
dipole makes with the electric field is:
(a) 300 (b) 600 (c) 450 (d) 900
3 In a moving coil galvanometer, the current in the coil is 1

(a) directly proportional to the angle of deflection.

(b) inversely proportional to the angle of deflection.
(c) directly proportional to the square root of the angle of deflection.
(d) inversely proportional to the square root of the angle of deflection.
4 An A.C. source is connected to a resistive circuit. Which of the following 1
statements is true?
(A) Current leads the voltage in phase
(B) Current lags the voltage in phase
(C) Current and voltage are in the same phase
(D) Either (A) or (B) depending on the value of resistance
5 The size of the atom is proportional to 1
1/3 2/3 - 1/3
(a) A (b) A (c) A (d) A
6 The relative permeability of iron is 6000. Its magnetic susceptibility is : 1
(a) 5999 (b) 6001 (c) 6000 x 10-7 (d) 6000 x 107
7 An ammeter of resistance 0.2 ohm and range 10 mA is to be used to read 1
potential difference up to 1V. It can be converted into a voltmeter of the
desired range by connecting
(a) 96 ohm in series
(b) 92 ohm in parallel
(c) 99.8 ohm in series
(d) 90 ohms in parallel
8 The work function of a metal is 4.2 eV, its threshold wavelength is : 1
(a)4000 Å (b) 3500 Å (c) 2945 Å (d) 2500 Å
9 Which of the following statements is incorrect about of photon? 1
(a) The energy of the photon is h𝛎.
(b) Photon energy is dependent on the intensity of radiation.
 (c) Photons are electrically neutral.
(d) The number of photons may not be conserved in a collision
10 An em wave is propagating in a medium with a velocity v = v i. The 1
instantaneous oscillating electric field of this wave is along the + y-axis. Then
the direction of the oscillating magnetic field of the em wave will be along
the:
(a) y axis (b) z axis (c) - z axis (d) - x axis
11 The current I in a coil varies with time as shown in figure below. 1

The variation of induced emf with time would be :

12 Which of the hydrogen line spectrum series belongs to the Ultraviolet region
of the electromagnetic spectrum
(a) Balmer series (b) Lyman Series (c) Paschen series (d) Brackett series
Directions for Q13 to Q16:
In the following questions, a statement of assertion is followed by a statement of
reason, Mark the correct choice as:
A) If both assertion and reason are true and reason is the correct explanation of
the assertion.
B) If both assertion and reason are true but the reason is the not correct
explanation of assertion.
C) If the assertion is true, the reason is false.
D) If both assertion and reason are false.
13 ASSERTION: No work is done in taking a positive charge from one point to 1
other inside a positively charged sphere while outside the sphere work is
 done in taking the charge toward the sphere.

REASON: Inside the sphere electric potential is same at each potential, but
outside it is different for different points.
14 ASSERTION: The light of a single frequency is incident on a metal surface, 1
the energies of emitted photoelectrons are different.

REASON: The energy of electrons emitted from inside the metal surface is
lost in collision with the other atoms in the metal.
15 ASSERTION: No interference pattern is detected when two coherent sources 1
are too close to each other.
REASON: The fringe width is inversely proportional to the distance between
the two slits.
16 ASSERTION: When a p-n junction diode is reverse biased, a feeble reverse 1

current flow is known as reverse saturation current.

REASON: In reverse bias condition, the minority carries can cross the
junction
SECTION – B
17 Draw energy band diagrams of n-type of p-type semiconductors at
temperature T > 0 K. Mark the donor and acceptor energy levels with their
energies.
18 Define the terms (i) ‘cut-off voltage’ and (ii) ‘threshold frequency’ in relation to 2

the phenomenon of the photoelectric effect. Using Einstein’s photoelectric

equation shows how the cut-off voltage and threshold frequency for a given
photosensitive material can be determined with the help of a suitable
plot/graph.
19 Draw a schematic ray diagram of an astronomical telescope showing how 2
rays coming from a distant object are received at the eye piece. Write two
advantages of a reflecting telescope over a refracting telescope.
Or
Write the generalized expression for the Ampere’s circuital law in terms of
the conduction current and the displacement current. Mention the situation
when there is:
(i) only conduction current and no displacement current.
(ii) only displacement current and no conduction current
20 Derive an expression for the drift velocity of free electrons in a conductor in 2
terms of relaxation time.
21 Calculate the binding energy per nucleon of Fe5626. 2

Given mFe = 55.934939 u, mn = 1.008665 u and mp = 1.007825 u

SECTION - C
22 State ‘Gauss law’ in electrostatics. Use this law to derive an expression for 3
the electric field due to an infinitely long straight wire of linear charge density
λ cm–1.
23 State Kirchhoff’s rules. Use Kirchhoff’s rules to determine the potential 3

difference between the points A and D when no current flows in the arm BE
of the electric network shown in the figure.

24 State the principle of working of a moving coil galvanometer. Also write 3

formula of its current sensitivity.
(i) What is the function of uniform radial field and how is it produced in a
moving coil galvanometer?
(ii) Why is it necessary to introduce a cylindrical soft iron core inside the coil
of a galvanometer?
25 Two concentric circular coils, one of small radius 𝑟1 and the other of large 3
radius 𝑟2 such that 𝑟1 ≪ 𝑟2 are placed co-axially with centres coinciding.
Obtain the mutual inductance of the arrangement. Give two factors on which
the coefficient of mutual inductance between a pair of coils depends.
Or,
Show diagrammatically how an alternating emf is generated by a loop of wire
rotating in a magnetic field. Write the expression for the instantaneous value
of the emf induced in the rotating loop.

26 Which constituent radiations of the electromagnetic spectrum is used - 3

(i) in RADAR systems used in aircraft navigation

(ii) in photographs of internal parts of the human body/as a diagnostic tool in
medicine
(iii) for taking photographs of sky, during night and fog conditions.
Give reason for your answer in each case.
27 The ground state energy of the hydrogen atom is – 13.6 eV. If an electron 3
makes a transition from an energy level of – 1.51 eV to – 3.4 eV, calculate
 the wavelength of the spectral line emitted and name the series of hydrogen
spectrum to which it belongs.
28 With the help of a ray diagram, show the formation of the image of a point 3
object due to refraction of light at a spherical surface separating two media
of refractive indices n1 and n2 (n2 > n1) respectively. What happens to the
focal length of a convex lens when it is immersed in water?
SECTION – D Case Study Questions
29 A prism is a portion of a transparent medium bounded by two plane faces 4
inclined to each other at a suitable angle. A ray of light suffers two
refractions on passing through a prism and hence deviates through a certain
angle from its original path. The angle of deviation of a prism is, δ = (μ- 1)
A, through which a ray deviates on passing through a thin prism of small
refracting angle A
(i) For which colour, angle of deviation is minimum? 1
(a) Red (b) Yellow (c) Violet (d) Blue
OR
When does white light move through vacuum?
(a) all colours the have same speed
(b) different colours have different speeds
(c) violet has more speed than red
(d) red has more speed than violet.
(ii) The deviation through a prism is maximum when angle of incidence is 1
(a) 45° (b) 70° (c) 90° (d) 60°
(iii) A ray of light falling at an angle of 50° is refracted through a prism and
suffers minimum deviation. If the angle of prism is 60°, then the angle of
minimum deviation is
(a) 45° (b) 75° (c) 50° (d) 40°
iv) If at i = 320 , the prism suffers an angle of minimum deviation. Find
angle of emergence e at i =250 .
(a) 390 (b) 380 (c) 370 (d) 410
30 Ge - semiconductor device 4
Base your answer to the following questions on the diagram below, which
represents a germanium semiconductor device.
 (i) In the diagram, section A represents the
(a) n-type Ge
(b) p-type Ge
(c) anode
(d) diode
(ii) The bias of the p-n junction shown in the diagram is
(a) C to D (b) E to F
(c)Reverse (d) Forward
To a germanium crystal equal number of aluminium and indium atoms are
added, then
(a) It remains an intrinsic semiconductor
(b) It becomes an n-type semiconductor
(c) It becomes a p-type semiconductor
(d) It becomes an insulator
Or

If Ge is doped with arsenic, that will result in

(a) n-type semiconductor
(b) p-type semiconductor
(c) intrinsic semiconductor
(d) none of these

(iii) Carbon, silicon and germanium have four valence electrons

each.These are characterized by valence and conduction
bands separated by energy band gaps respectively equal
to (Eg)C, (Eg)Si and (Eg)Ge. Which of the following
statements is true?

(a) (Eg)Si < (Eg)Ge < (Eg)C

(b) (Eg)C < (Eg)Ge > (Eg)Si
(c) (Eg)C > (Eg)Si > (Eg)Ge
(d) (Eg)C = (Eg)Si = (Eg)Ge
SECTION – E
31 (a) Find an expression for the electric field strength at a distant point 5

situated along the equatorial line of an electric dipole. (3)

 (b) A point charge + 10 µC is at a distance 5 cm directly above the the
centre of a square of side 10 cm as shown in figure. What is the magnitude
of the electric flux through the square? 2

Or
(a) Briefly explain the principle of a capacitor. Derive an expression for the
capacitance of a parallel plate capacitor, whose plates are separated by a
dielectric medium. 3
(b) Find the equivalent capacitance of the network shown in the figure, when
each capacitor is of 1 µF. When the ends X and Y are connected to a 6 V
battery, find out (i) the charge and (ii) the energy stored in the network. (2)

32 (a) Two harmonic waves of monochromatic light 𝒚𝟏 = 𝒂 𝐜𝐨𝐬 𝝎𝒕 and 𝒚𝟐

𝐜𝐨𝐬(𝝎𝒕 + 𝝓), are superimposed on each other. Show that the maximum
intensity in the interference pattern is four times the intensity due to each
slit.
(b) Also write the condition for constructive and destructive interference in
terms of the phase angle 𝜙.
Or
(a) Using Huygens’s principle draw a diagram to show how a plane wave
front incident at the interface of the two media gets refracted when it
propagates from a rarer to a denser medium. Hence Verify Snell’s law of
refraction.
(b) Two coherent sources have intensities in the ratio 25:16. Find the ratio of
intensities of maxima to minima after interference of light occurs.
 33 A ‘X′ is connected to an ac source V = V0 sinωt.The current I = I0 sin(ωt -2 ). 5
𝜋

The variation of voltage, current and power in one cycle is shown in the
following graph :

(i) Identify the device ‘X′.

(ii) Which of the curves A, B and C represent the voltage, current and power
in the circuit? Justify your answer.
(iii) How does its impedance vary with the frequency of the ac source? Show
graphically.
(iv) Obtain the expression for the current in the circuit and its phase relation
with ac voltage.
(v) At very high-frequency a.c., the capacitor behaves as a conductor. Why?
OR
(a) Describe briefly, with the help of a labelled diagram, the working of a
step-up transformer. 3
(b) Write any two sources of energy loss in a transformer. 1
(c) A step-up transformer converts a low voltage into a high voltage. Does it
not violate the principle of conservation of energy? Explain. 1

Answer key to MCQs

1a 2a 3a 4 c 5 b 6 b 7 c 8 c 9 b 10 b 11 d 12 b