अनक्र

ु म ांक/ROLL NO सेट / SET: 4

केंद्रीय विद्यालय संगठन ,जयपरु संभाग

KENDRIYA VIDYALAYA SANGATHAN, JAIPUR REGION

PRACTICE EXAM :2024-25

कक्ष / CLASS: XII
विषय /SUB: PHYSICS (कोड / CODE:042)
अधिकतम आिधि / Time Allowed: 3 Hours अधिकतम अांक / Maximum Marks: 70
स म न्य ननर्दे श / General Instructions:
(1) There are 33 questions in all. All questions are compulsory.
(2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
(3) All the sections are compulsory.
(4) Section A contains sixteen questions, twelve MCQ and four Assertion Reasoning based questions of 1 mark
each, Section B contains five questions of two marks each, Section C contains seven questions of three marks
each, Section D contains two case study-based questions of four marks each and Section E contains three long
answer questions of five marks each.
(5) 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.
(6) Use of calculators is not allowed.
(7) You may use the following values of physical constants where ever necessary
a. C = 3 x108 m/s
b. Me = 9.1x10-31 kg
c. Mp = 1.7x10-27 kg
d. e = 1.6x10-19 C
e. µ0 = 4πx10-7 Tm𝑨−𝟏
f. h = 6.63 x10-34 Js
g. ε0 = 8.854 x10-12 𝑪𝟐𝑵−𝟏𝒎−𝟐
h. Avogadro’s number = 6.023X𝟏𝟎𝟐𝟑 per gram mole

SECTION-A
1. A parallel plate capacitor is charged by a battery after charging the capacitor, battery is 1
disconnected and decrease the distance between the plates then which following statement
is correct?
(A) electric field is not constant
(B) potential difference is increased
(C) decrease the capacitance
(D) decrease the stored energy
2. If 50 Joule of work must be done to move electric charge of 2C from a point, where potential 1
is +10 volt to another point, where potential is V volt, find the value of V-
(A) 5 (B) –15 V (C) +35 V (D) +10 V

Page 1
3. A long straight wire of radius 'a' carries a steady current i. The current is uniformly 1
a
distributed across its Cross section. The ratio of the magnetic field at and 2a distances is-
2
(A) 4 (B) 1 (C)1/2 (D) 1/4
4. What happens, when the width of the slit aperture is increased in an experiment of single slit 1
diffraction experiment-
(A) spread of diffraction region is increased
(B) spread of diffraction region is decreased
(C) spread of diffraction region will be decreased and mid-band becomes narrow
(D) none of the above
5. The electromagnetic waves used in radar systems are- 1
(A) Infrared waves (B) Ultraviolet rays
(C) Microwaves (D) X-rays
6. In a series resonant LCR circuit, the voltage across R is 100 volts and R = 1 kΩ with C = 2 1
μF. The resonant frequency ω is 200 rad/s. At resonance the voltage across L is -
(A) 250 V (B) 4 × 10–3 V
(C) 2.5 × 10–2 V (D) 40 V
7. A welder wears special glasses to protect his eyes mostly from the harmful effect of – 1
(A) Infrared waves (B) Ultraviolet rays
(C) Microwaves (D) very intense visible light
8. For nuclei with A > 100, mark the incorrect statement - 1
(A) the binding energy per nucleon decreases on the average as A increases
(B) if the nucleus breaks into two roughly equal parts, energy is released
(C) if two nuclei fuse to form a bigger nucleus energy is released
(D) the nucleus with Z > 83 are generally unstable
9. Find the new focal length of convex lens of focal length 20cm and refractive index 1.5 when 1
it is immersed in water (refractive index of the water is 4/3)
(A) 5 cm (B) 80 cm (C) 60 cm (D) 120 cm
10. Which of the following is incorrect about interference pattern in a Young’s double slit 1
experiment?
(A) The intensity of all bright fringes is same
(B) The central maximum is that at which phase difference between interfering waves is
zero
(C) For observing interference pattern, first diffraction must take place
(D) The beams producing interference must have zero phase difference
11. The difference in the variation of resistance with temperature in a metal and a semiconductor 1
arises essentially due to the difference in the –
(A) Variation of the number of charge carriers with temperature
(B) Type of bonding
(C) Variation of scattering mechanism with temperature
(D) Crystal structure

Page 2
12. The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease 1
in diameter the change in the resistance of the wire will be-
(A) 300% (B) 200%
(C) 100% (D) 50%
For Questions 13 to 16, two statements are given –one labelled Assertion (A) and other labelled
Reason (R). Select the correct answer to these questions from the options as given below.

A. If both Assertion and Reason are true and Reason is correct explanation of Assertion.
B. If both Assertion and Reason are true but Reason is not the correct explanation of
Assertion.
C. If Assertion is true but Reason is false.
D. If both Assertion and Reason are false.
13. Assertion: The ferromagnetic substance do not obey Curie's law. 1
Reason: At Curie point a ferromagnetic substance start behaving as a paramagnetic
substance.
14. Assertion: Energy is released in nuclear fission. 1
Reason: Total binding energy of the fission fragments is larger than the total binding energy
of the parent nucleus.
15. Assertion: Kinetic energy of photoelectrons emitted by a photosensitive surface depends 1
upon the intensity of incident photon.
Reason : The ejection of electrons from metallic surface is possible with frequency of
incident photon below the threshold frequency
16. Assertion: A particle can behave both as a particle and wave but in a given situation, it 1
behaves either as a particle or as a wave.
Reason: A photon and an electron have same wavelength, then the velocity of photon is less
than that of the electron.
SECTION-B

17. (a) In hydrogen atom an electron undergoes transitions from 2nd excited state to the 1st 2
excited state and then to the ground state. Identify the spectral series to which transition
belong.
(b) Find out the ratio of the wavelength of the emitted radiations in the two cases.

OR
Using Rutherford model of the atom, derive the expression for the total energy of the electron
in hydrogen atom
18. When two waves of equal amplitude and frequency interfere each other then find the ratio 2
of intensity when the two waves arrive in phase to that when they arrive 90  .
19. Two very long, straight and parallel wires carry steady currents I and I respectively. The 2
distance between the wires is d. At a certain instant of time, a point charge q is at a point
equidistant from the two wires in the plane of the wires. Its instantaneous velocity v is
perpendicular to this plane. Find the magnitude of the force due to the magnetic field acting
on the charge.
Page 3
20. If a nucleus 26Fe56 splits into two nuclei of 13 Al28, would the energy be released or needed for 2
this purpose to occur? Given m (26 Fe56) = 55.934944&m (13 Al28) = 27.98191,
1u = 931MeV/c2,Calculate the energy in MeV.
21. Two cells of EMF 1V, 2V and internal resistances 2Ω and 1Ω respectively are connected in (i) 2
series, (ii) parallel. What should be the external resistance in the circuit so that the current
through the resistance be the same in the two cases? In which case more heat is generated
in the cells?
SECTION C
22. A germanium crystal is doped with antimony. With the help of energy band diagram, explain 3
how the conductivity of the doped crystal is affected.

23. A parallel plate capacitor of capacitance C is charged to a potential V. It is then connected to 3

another uncharged capacitor having the same capacitance. Find out the ratio of the energy
stored in the combined system to that stored initially in the single capacitor.
24. What are optical fibers? Draw a labelled diagram of an optical fiber and show how light 3
propagate through the optical fiber using this phenomenon. Mention their one practical
application.
25. Describe briefly, with the help of a diagram, the role of the two important processes 3
involved in the formation of a p-n junction. How the depletion layer formed.
26. With the help of a circuit, show how a moving coil galvanometer can be converted into an 3
voltmeter.
To convert a given galvanometer into a voltmeter of ranges 2V, V and V/2 volt, resistance R1,
R2 and R3 ohm respectively, are required to be connected in series with the galvanometer.
Obtain the relationship between R1 , R2 and R3.
27. Define wavefront. Using Huygen’s principle to verify the laws of reflection. 3
OR
State Huygen’s postulates of wave theory. Using this verify the laws of refraction.
28. An infinitely long positively charged straight conductor of linear charge density . An 3
electron is revolving in a circle with a constant speed v such that the wire passes through the
Centre, and is perpendicular to the plane, of the circle. Find the kinetic energy of the electron
in term of q &.
Draw a graph of kinetic energy as a function of linear charge density .
SECTION D
29. Case Study Based Question : Loudspeakers - Motion of Charge in Magnetic Field

A common application of the magnetic force on a current carrying conductor wire is found
in loudspeakers. A loudspeaker consists of permanent magnets, basket, voice coils, flexible
suspension & rigid speaker cone as shown in figure.
A light voice coil is mounted so that it can move freely inside the magnetic field of a strong
permanent magnet. The paper cone is attached to the voice coil and attached with a flexible
mounting to the outer ring of the support .Because there is a definite equilibrium position
for the speaker cone and there is elasticity of the mounting structure, there is inevitably a

Page 4
 free cone resonant frequency like of a mass on a spring. The frequency can be determined by
adjusting the mass and stiffness of the cone and voice coil.
The magnetic field created by the permanent magnet exerts a force on the voice coil that is

proportional to the current in coil. The ratio drives a rapidly changing current through the
coil. The current follows that vibrations of speech and the electromagnetic force follows the
current changes, pushing the paper cone. Finally the air in front of the loudspeaker is set into
vibration following the cone's motion, and sound waves are transmitted to the listener

The ratio drives a rapidly changing current through the coil. The current follows that
vibrations of speech and the electromagnetic force follows the current changes, pushing the
paper cone. Finally the air in front of the loudspeaker is set into vibration following the cone's
motion, and sound waves are transmitted to the listener.
i. Loudspeaker works on the principle of 1
(A) Detector (B) Generator (C) Amplifier (D) Motor
ii. Electrodynamic speaker can handle which type of audio power relative to permanent 1
magnet type speaker?
(A) Lower (B) Equal (C) Higher (D) Both a and b
iii. To increase the power handling capacity in loudspeakers which type of magnet is used?
(A) Temporary magnet (B) Permanent magnet (C) Electromagnet (D) None of these
IV. A horizontal wire 0⋅1m long carries a current of 5A. Find the magnitude and direction of the 1
magnetic field, which can support the weight of the wire. Given the mass of the wire
is 3×10−3kg/m and g=10ms−2.
(A) 6×10−3T, acting vertically upwards
(B) 6×10−3T, acting horizontally perpendicular to wire
(C) 6×10−2T, acting vertically downwards
(D) 6×10−2T, acting horizontally perpendicular to wire
OR
A square current carrying loop is suspended in a uniform magnetic field acting in the plane
of the loop. If the force on one arm of the loop is →, the net force on the remaining three arms
𝐹
of the loop is
(A) → (B) → (C) → (D) →
𝐹 −𝐹 3𝐹 −3𝐹

30. Case Study Based Question : Photoelectric Effect

Page 5
 In 1887, German physicist Heinrich Hertz noticed that shining a beam of ultraviolet light
onto a metal plate could cause it to shoot sparks. It is due to the emission of negatively
charged particles called electrons from the metal surface into the surrounding space.
Hallwachs and Lenard also observed that when ultraviolet light fell on the emitter plate, no
electrons were emitted at all when the frequency of the incident light was smaller than a
certain minimum frequency. Experimental study shows that different metals required
different minimum frequencies of light for the emission of electron. When brightness of the
incident light increases, more electrons were produced, without increasing their energy,
and increasing the frequency of the light produced electrons with higher energies, but
without increasing the number produced. This is known as the photoelectric effect, and it
would be understood in 1905 by a young scientist named Albert Einstein.
i. In photoelectric effect, the kinetic energy of emitted electrons from the metal surface 1
depends upon
(A) frequency of incident light
(B) velocity of incident light
(C) intensity of light
(D) angular momentum of emitted electron
ii. With the increase of intensity of incident radiations on photoelectrons emitted by a photo 1
tube, the number of photoelectrons emitted per unit time is
(A) increases (B) decreases
(C) remains same (C) none of these
iii. A point source of light of power 3.2 x 10-3 W emits monenergistic photons of energy 5.0 eV 1
and work function 3.0 eV. The efficiency of photoelectron emission is 1 for every 106
incident photons. Assume that photoelectrons are instantaneously swept away after
emission. The maximum kinetic energy of photon is
(A) 4 eV (B) 5 eV
(C) 2 eV (D) Zero
OR
A metal of work function 3·3 eV is illuminated by light of wavelength 300 nm. The
maximum kinetic energy of photoelectrons emitted is (taking h = 6·6 x 10-34 Js)
(A) 0.413 eV (B) 0.825 eV (C) 1.65 eV (D) 1.32 eV
IV. If frequency (v > v0) of incident light becomes n times the initial frequency (v), then K.E. of 1
the emitted photoelectrons becomes (v0 threshold frequency).
(A) n times of the initial kinetic energy
(B) More than n times of the initial kinetic energy
(C) Less than n times of the initial kinetic energy
(D) Kinetic energy of the emitted photoelectrons remains unchanged

SECTION E

31. A. State the condition under which a large magnification can be achieved in an astronomical 5
telescope.
B. Give the reasons to explain why a reflecting telescope is preferred over a refracting
telescope.
C. State two main considerations considered while choosing the objective of astronomical
telescope.
OR
Page 6
 A. Draw a labelled ray diagram for the formation of image by a compound microscope.
B. Derive an expression for its total magnification when the final image formed at the near
point.
C. Why both objective and eyepiece of a compound microscope must have short focal
lengths?

32. A. Explain with the help of a labelled diagram, the principle and working of an ac generator. 5
Write the expression and graphical representation for the emf generated in the coil in
terms of speed of rotation.
B. Can the current produced by an ac generator be measured with a moving coil
galvanometer? Why?
C. What is the source of energy generation in this device?
OR
A. Explain why the reactance provided by an inductor to an alternating current increase with
increasing frequency.
B. An electric lamp connected in series with a capacitor and an ac source is glowing with of
certain brightness. How does the brightness of the lamp change on reducing the capacitor
and frequency?
C. An inductor L of reactance XL is connected in series with a bulb B to a ac source. Explain
briefly how does the brightness of bulb change when number of turns of inductor
reduced

33. A. State Kirchhoff’s laws for an electrical network. Using Kirchhoff’s laws, find the relation 5
between the resistances of four arms of a Wheatstone bridge when the bridge is balanced.
B. What do you understand by ‘sensitivity of Wheatstone bridge’? How the sensitivity of
Wheatstone bridge can be increased.

OR

A. Define the term ‘mobility’ of charge carriers in a current carrying conductor. Obtain the
relation for mobility in term of relaxation time.
B. Why are alloys used for making standard resistance coils?
C. On what factors does conductivity of a conductor depends.

Page 7