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KENDRIYA VIDYALAYA SANGATHAN, HYDERABAD REGION
CLASS-12-PHYSICS MODEL QUESTION PAPER - 16 (2024-25)
MARKING SCHEME
Q. Answer Marks
No. awarded
[SECTION – A] (16x1=16 marks)
1 (a) planes parallel to YZ-plane 1 Mark
2 (a) A is + ve and B is – ve and |A|>|B| 1 Mark
3 (a) is towards West 1 Mark
4 (d) the same wavelength and constant phase difference 1 Mark
Explanation: Two light sources are said to be coherent when both light sources emit
light of the same wavelength and constant phase difference.
5 (d) 6 V 1 Mark
6 (c) leads the applied emf by angle π/2 1 Mark
7 (b) An accelerating charge 1 Mark
8 (b) 1 : –1 1 Mark
9 (b) separate the red colour part from the green and blue colours 1 Mark
10 (c) there shall be no interference fringes. 1 Mark
11 (a) electrons move from lower energy level to higher energy level in the conduction 1 Mark
band.
12 (a) 1 Mark
13 A. both Assertion and Reason are true and Reason is the correct explanation of 1 Mark
assertion.
14 C. Assertion is true but Reason is false. 1 Mark
15 C. Assertion is true but Reason is false 1 Mark
16 D. both Assertion and Reason are false. 1 Mark
Section B (07x2=14 marks)
17 The three characteristic features which cannot be explained by wave theory are: 1M
(i) Kinetic energy of emitted electrons is found to be independent of the
intensity of incident light.
(ii) (ii) There is no emission of electrons if frequency of incident light is below 0.5M
a certain frequency (threshold frequency).
(iii) (iii) Photoelectric effect is an instantaneous process. 0.5M
2
18 1M
1M
(or)
(a) Conditions for sustained interference:
(b) (i) The interfering sources must be coherent i.e., sources must have same
frequency and constant initial phase. 1M
(c) (ii) Interfering waves must have same or nearly same amplitude, so that there
may be contrast between maxima and minima
(d) Fringe width, β 1M
β If distance d between the slits is reduced, the size of fringe width will
increase.
19 Thus, electric and magnetic forces are in opposite 1M
directions. Suppose we adjust the values of E and B
such that magnitudes of the two forces are equal,
then the total force on the charge is zero and the
charge will move in the fields undeflected. This
happens when qE =qvB v or v=E/ B This condition can
be used to select charged particles of a particular 1M
velocity out of a beam containing charges moving
with different speeds (irrespective of their charge and
mass). The crossed E and B fields therefore serve as a
velocity selector. Trajectory becomes helical about
the direction of magnetic field .
20 1M
1M
Conclusions: (i) The potential energy is minimum at a distance r0 of about 0.8 fm.
(ii) Nuclear force is attractive for distance larger than r0. (iii) Nuclear force is repulsive
if two are separated by distance less than r0. (iv) Nuclear force decreases very rapidly
at r0, equilibrium position.
21 (i) When a potential difference is applied across a conductor, an electric field is 1M
produced and free electrons are acted upon by an electric force (Fe). Due to this,
electrons accelerate and keep colliding with each other and acquire a constant
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(average) velocity vd called drift velocity. Electric force on electron Fe =– eE. If m is
the mass of electron, then its acceleration (ii) With rise of temperature, the rate of
collision of electrons with ions of lattice increases, so relaxation time decreases. As a
result the drift velocity of electrons decreases with the rise of temperature. 1M
Section C
22 Bulb B1 will glow as diode D1 is forward biased. . 1M
Reason with explanation 1M+1M
23 1M
1M
1M
24 a) Compound Microscope: 0.5M
Adjustment: 0.5M
Working: 0.5M
Magnifying power 0.5 M
1M
Ray diagram
25 Rectification: Rectification means conversion of ac into dc. A p-n diode acts as a 1M
rectifier because an ac changes polarity periodically and a p-n diode allows the current
to pass only when it is forward biased. This makes the diode suitable for rectification
Working: Working (i) During positive half cycle of input alternating voltage, the diode
is forward biased and a current flows through the load resistor R2 and we get an
output voltage. (ii) During other negative half cycle of the input alternating voltage,
the diode is reverse biased and it does not conduct (under break down region). Hence,
ac voltage can be rectified in the pulsating and unidirectional voltage. 1M
1M
26 Moving coil galvanometer: A galvanometer is used to detect current in a circuit. 1M
Construction: It consists of a rectangular coil wound on a non-conducting metallic
frame and is suspended by phosphor bronze strip between the pole-pieces (N and S)
of a strong permanent magnet. A soft iron core in cylindrical form is placed between
the coil. One end of coil is attached to suspension wire which also serves as one
terminal (T1) of galvanometer. The other end of coil is connected to a loosely coiled
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strip, which serves as the other terminal (T2). The other end of the suspension is
attached to a torsion head which can be rotated to set the coil in zero position. A 1M
mirror (M) is fixed on the phosphor bronze strip by means of which the deflection of
the coil is measured by the lamp and scale arrangement. The levelling screws are also
provided at the base of the instrument. The pole pieces of the permanent magnet are
cylindrical so that the magnetic field is radial at any position of the coil.
Principle and working: When current (I) is passed in the coil, torque τ acts on the coil, 1M
given by τ =NIAB sin θ where θ is the angle between the normal to plane of coil and
the magnetic field of strength B, N is the number of turns in a coil. A current carrying
coil, in the presence of a magnetic field, experiences a torque, which produces
proportionate deflection. i.e., Deflection, θ ∝τ (Torque) When the magnetic field is
radial, as in the case of cylindrical pole pieces and soft iron core, then in every position
of coil the plane of the coil, is parallel to the magnetic field lines, so that θ =90° and sin
90°=1. The coil experiences a uniform coupler. Deflecting torque, τ = NIAB If C is the
torsional rigidity of the wire and is the twist of suspension strip, then restoring torque
= C θ For equilibrium, deflecting torque = restoring torque i.e. NIAB = C θ .
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1M
1M
1M
28 (a) Electric flux is defined as the number of electric field lines passing through an 0.5M
area normal to the surface. Alternatively. The surface integral of the electric field is
defined as the electric flux through a closed surface.
0.5M
1M
5
OR
1M
Section D
29 i-c 1M
ii-c 1M
iii-d 1M
iv-c (or) v-b 1M
30 i-a 1M
ii-b 1M
iii-c 1M
iv-b (or) v-d 1M
Section E
31 State Kirchhoff’s rules for electrical networks (1M+1M)
of Wheatstone bridge circuit- 1M
condition- 1M
formula– 1M
(OR)
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1M
1M
1M
1M
1M
32 labelled diagram- 1M-
principle 1M
working- 1M
expression - 1M
graph showing variation of emf 1M
(OR)
Circuit diagram- 1M-
phasor diagram- 1M
condition for resonance- 1M
resonating frequency- 1M
peak current (imax) with frequency- 1M
33 Given fo = 4 cm, fe = 10 cm uo = – 6 cm Magnifying power of microscope 1M
1M
1M
1M
1M
Length of microscope L = | vo | + | ue|= 19.14 cm
(OR)
Derive the mirror formula 2M
formula for a thin lens 1M
Draw a ray diagram- 1M
magnification formula- 1M
