ISC Class 12 Physics Sample Paper For Half Yearly Exam 2025

Section A

14

Section B

14

Section C

27

Section D

15

Total Marks

70

Question No.

Section A

1. A.

In questions (i) to (vii) below, choose the correct alternative (a), (b), (c) or (d) for each of the questions given below :

I. For a series L-C-R circuit, I vs w curve is shown :

(A) To the left of w , the circuit is mainly capacitive. r

(B) To the left of w , the circuit is mainly inductive. r

(C) At w , impedance of the circuit is equal to the resistance r

of the circuit.

(D) At w , impedance of the circuit is 0.

Choose the most appropriate answer from the options given below.

(a) (A) and (D) only

(b) (B) and (D) only.

(c) (A) and (C) only.

(d) (B) and (C) only.

ii. Assertion A: The Curie temperature is the temperature above which a ferromagnetic material becomes paramagnetic.

Reason R : Above the Curie temperature, the thermal energy overcomes the magnetic energy that align with magnetic dipole.

In the light of the above statements, choose the correct answer from the options given below.

(a) Both Aand B are true and R is the correct explanation of A.

(b) Both Aand B are true but R is not the correct explanation of A.

(c) Ais true but R is false.

(d) Ais false but R is true.

iii. In a coil of resistance 100 W, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is

(a) 275 Wb

(b) 200 Wb

(c) 225 Wb

(d) 250 Wb

iv. In single slit diffraction experiment, two waves reaching at P from A and B (as shown in figure) have path difference . At P one observe :

(a) first secondary minimum

(b) first secondary maximum

(c) second secondary minimum

(d) second secondary maximum.

v. A point charge + q is placed at the origin O as shown in the figure. Work done in taking another point charge - Q from point A(0, a) to another point B (a, 0) along the straight path AB is :

vi. Given below are two statements : One is labelled as Assertion Aand the other is labelled as Reason R.

Assertion A: Alloys such as constantan and manganin are used in making standard resistance coils.

Reason R : Constantan and manganin have very small value of temperature coefficient of resistance.

In the light of the above statements, choose the correct answer from the options given below.

(a) Both A and B are true and R is the correct explanation of A.

(b) Both A and B are true, but R is not the correct explanation of A.

(c) A is true but R is false.

(d) A is false but R is true.

Vii.A circular coil having N turns of radius R carries a current I and produces a magnetic field T at its

centre O. If the coil is opened and rewound such that the radius of the newly formed coil is 2R and the same current I is passed through it, the magnetic field at the centre O will be :

(a) 2T

(b) T

(c)T/2

(d)T/4

B. 

Answer the following questions briefly and to the point :

I. A metallic sphere is placed in a uniform electric field. Which path is followed by the lines of force shown in figure ?

Ii. The voltage current variation of two metallic wire X and Y at constant temperature are shown in the figure. Assuming that the wires have the same length and the same diameter, explain which of the two wires will have larger resistivity?

Iii. Can two sodium vapour lamps act as a coherent source?

Iv. 

V.Define Ampere, in terms of force between two current-carrying conductors.

Vi.

Vii. State Biot-Savart’s Law in vector form.

SECTION - B

(a) What is meant by Wattless current ?

(b) Draw a labelled graph showing the vaiation of impedance (Z) of a series L-C-R circuit versus

frequency of the AC supply.

3.

A power transmission line feeds input power at 2300 V to step down transformer with primary windings

having 4000 turns. The output power is delivered at 230 V by the transformer. If the current in the primary of

the transformer is 5Aand its efficiency is 90%, what is the output current ?

4.

OR

The following graph shows the variation of terminal potential difference V, across a combination of three

cells in series to a resistor versus current I :

(a) Calculate the emf of each cell.

(b) For what current I, will the power dissipation of the circuit be maximum ?

5.

In Young’s double slit experiment with monochromatic light, how is the fringe-width affected if :

(a) Young’s apparatus is immersed in water.

(b) The separation d between the two slits is doubled and the distance D of the screen from the slit is halved.

6.

(a) What is ‘radial field’?

(b) How can a moving coil galvanometer be converted into an ammeter ?

7.

(a) What is the wavelength range of electromagnetic radiation used in radio broadcast ?

(b) State Curie’s Law.

8.

SECTION - C

9.

A current of 4Aflows in a coil when connected to a 12 VDC source. If the same coil is connected to a 12V-

8 Hz AC source, a current of 2.4 Aflows in the coil. Calculate :

(i) Inductive reactance of the coil.

(ii) Coefficient of self-inductance (L) of the coil.

10.

A student is performing an experiment on single slit diffraction. The examiner gives the following instructions to the student. State whether the responses of the student, in each case, are correct or incorrect.

Give a reason for your answer.

(i) EXAMINER: Increase the intensity of the diffraction bands.

STUDENT: Increases the width of the slit.

(ii) EXAMINER: Place a tiny circular obstacle in the path of light from a distant source. Describe the result of your observation.

STUDENT: A bright spot is seen at the centre of the shadow of the obstacle.

(iii) EXAMINER: Increase the linear width of the central maximum of the single slit diffraction pattern.

STUDENT: Increases the width of the slit.

11.

(a) For observing Fraunhofer diffraction from a single slit, what type of wavefront should be incident on

the slit?

(b) State one similarity between interference and diffraction of light.

(c) Draw a labelled graph to show variation in intensity with (q) in the Fraunhofer diffraction experiment for a single slit diffraction.

12.

A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes in

Young’s double-slit experiment on a screen 1 m away. The separation between the slit is 1 mm.

(i) Find the distance of the third bright fringe on the screen from the central maximum for the wavelength 650 nm.

(ii) What is the least distance from the central maximum when the bright fringes due to both the wavelengths coincide? 

13.

A potentiometer wire of length 1 m is connected to a driver cell of emf 3V as shown in the figure. When a cell of

1.5 V emf is used in the secondary circuit, and the balance point is found to be 60 cm. On replacing this cell and using a cell of unknown emf, the balance point shifts to 80 cm.

(i) Calculate the unknown emf of the cell.

(ii) Explain with reason, whether the circuit works, if the driver cell is replaced with a cell of emf 1 V.

(iii) Does the high resistance R, used in the secondary circuit affect the balance point ? Justify your answer.

OR

A potential difference V exists across a copper wire of length l and diameter d. How will the drift velocity be affected if

(i) V is doubled

(ii) l is doubled

(iii) d is doubled.

14.

A parallel plate capacitor of capacitance C is charged to a potential V by a battery. Without disconnecting the battery, the distance between the plates is tripled and a dielectric medium of (K = 10) is introduced between

the plates of the capacitor. Explain giving reason, how will the following be affected :

(a) Capacitance of the capacitor.

(b) Charge on the capacitor.

(c) Energy density of the capacitor.

15.

Derive an expression for the force experienced by a current-carrying straight conductor placed in a uniform magnetic field.

16.

(a) Write the Lorentz force in vector form.

(b) A uniform magnetic field gets modified as shown below, when two specimens X and Y are placed in it.

(i) Identify the two specimen X and Y.

(ii) What will be the susceptibility of specimen X and Y?

17.

OR

Section D

18.

(a) With the help of appropriate diagrams, derive the relation e = Bl v for the motional emf produced in the wire of length l, moving with velocity v, perpendicular to a uniform magnetic field.

(b) Along solenoid with 15 turns per cm has a small loop of area 2.0 cm placed inside, normal to the axis of the solenoid. The current carried by the solenoid changes steadily from 2A to 4A in 0.1 s. What is the induced emf in the loop while the current is changing?

OR

19.

Read the passage(s) and answer the following questions:

Huygens, the Dutch physicist and astronomer of the seventeenth century, gave a beautiful geometrical description of wave propagation. Consider a source of light S, placed in an isotropic medium. This source sends out waves in all directions, which propagate with the same speed c in these directions. After time ‘t’the disturbance will lie on the surface of a sphere of radius ct. This spherical surface is called a wavefront. Huygens' idea is that we can think of every oscillating point on a wavefront as a new source of waves. According to Huygens' principle, what we observe is the result of adding up the waves from all these new sources.

A wavefront is defined as the surface of constant phase. The speed with which the wavefront moves outward from the source is called the phase speed. The energy of the wave travel in a direction perpendicular to the wavefront.

(i) What is the phase difference between any two points lying on a wavefront?

(ii) Light always travel, making an angle ‘q’with the wavefront. What is the value of q?

(iii) On the basis of Huygen’s wave theory, show that when light is incident on a plane mirror obliquely,

angle of reflection is equal to angle of incidence.

20.

(a) Derive an expression for the intensity of the electric field at a point in end-on position i.e., axial position of an electric dipole. 

(b) Along wire is bent as shown. Find the magnitude and direction of the magnetic field at the centre O of the circular part, if a current of I ampere is passed through the wire.

OR