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Physics (Theory) Official Board Paper 2025-2026 ISC (Science) ISC Class 12 Question Paper Solution

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Physics (Theory) [Official Board Paper]
Marks: 70 CISCE
ISC (Science)

Academic Year: 2025-2026
Date & Time: 16th March 2026, 2:00 pm
Duration: 3h
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Instructions to Candidates

  1. You are allowed an additional fifteen minutes for only reading the question paper. 
  2. You must NOT start writing during reading time.
  3. This question paper has 11 printed pages and one blank page.
  4. There are twenty questions in this paper. Answer all questions.
  5. There are four sections in the paper: A, B, C and D. Internal choices have been provided in two questions each in Sections B, C and D.
  6. Section A consists of one question having fourteen subparts of one mark each.
  7. While attempting Multiple Choice Questions in Section A, you are required to write only ONE option as the answer.
  8. Section B consists of seven questions of two marks each.
  9. Section C consists of nine questions of three marks each.
  10. Section D consists of three questions of five marks each.
  11. The intended marks for questions are given in brackets [ ].
  12. A list of useful constants and relations is given at the end of this paper.
  13. A simple scientific calculator without a programmable memory may be used for calculations.

Instruction to Supervising Examiner

  1. Kindly read aloud the Instructions given above to all the candidates present in the examination hall.


SECTION - A (14 Marks)
[7]1. (A) | In questions (i) to (vii) given below, choose the correct alternative (a), (b), (c) or (d).
[1]1. (A) (i)

A fish called an electric eel can generate a voltage up to 800V. If it can supply a current of 5mA, the maximum power it can deliver is ______.

4000 W

400 W

40 W

4 W

Concept: undefined - undefined
Chapter:
[1]1. (A) (ii)

A collimated beam of protons is travelling with a constant velocity along X-axis There is a current carrying solenoid whose axis is also X-axis. If the beam now enters the solenoid along its axis, it will ______

describe a circular path.

get deflected along Z-axis.

get deflected along Y-axis.

continue to travel undeflected.

Concept: undefined - undefined
Chapter:
[1]1. (A) (iii)

An electron, a proton, a deuteron and an alpha particle are all accelerated from rest through the same potential difference. Which one will have the maximumde Broglie wavelength?

Proton

Deuteron

Electron

Alpha particle

Concept: undefined - undefined
Chapter:
[1]1. (A) (iv)

Magnetic susceptibility (Ψ) of a material is found to decrease with the rise in its temperature. The material is ______

diamagnetic.

paramagnetic.

ferromagnetic.

not magnetic.

Concept: undefined - undefined
Chapter:
[1]1. (A) (v)

When a p-n junction diode is forward-biased ______

it acts as an insulator and no current flows through it.

it offers a low resistance and a large current flows through it.

it offers a high resistance and a small current flows through it.

the width of depletion region increases.

Concept: undefined - undefined
Chapter:
[1]1. (A) (vi)

When a biconvex lens of glass of refractive index 1.6 was dipped in a certain transparent liquid, it was found to behave like a plane sheet of glass. So, the refractive index of the liquid is ______.

1.0

1.4

1.5

1.6

Concept: undefined - undefined
Chapter:
[1]1. (A) (vii) | Given below are two statements marked, Assertion and Reason. Read the two statements and choose the correct option.

Assertion: In Young’s double slit experiment, the first bright band for blue light is closer to the centre than the first bright band for green light.

Reason: Blue light has a longer wavelength than green light.

Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

Both Assertion and Reason are true but Reason is not the correct explanation for Assertion.

Assertion is true and Reason is false.

Assertion is false and Reason is true.

Concept: undefined - undefined
Chapter:
[7]2. (B) | (B) Answer the following questions briefly:
[1]2. (B) (i)

Calculate the momentum of a photon having an energy of 4.8 × 10−19 J.

Concept: undefined - undefined
Chapter:
[1]2. (B) (ii)

What is motional emf?

Concept: undefined - undefined
Chapter:
[1]2. (B) (iii)

Calculate work done in moving a point charge ‘q’ through a distance ‘d’ along perpendicular bisector of an electric dipole, which consists of two-point charges −Q and +Q separated by a distance ‘L’.

Concept: undefined - undefined
Chapter:
[1]2. (B) (iv)

Draw the symbol of a Zener diode.

Concept: undefined - undefined
Chapter:
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[1]2. (B) (v)

A thin convex lens of power 5 D is kept in contact with a thin concave lens of power 8 D. Calculate the focal length of the combination.

Concept: undefined - undefined
Chapter:
[1]2. (B) (vi)

The image below shows a compound microscope. Which one of the two lenses L1 or L2 has a larger focal length?

Concept: undefined - undefined
Chapter:
[1]2. (B) (vii)

Radius of the first Bohr orbit of hydrogen atom is 0.05nm. Calculate the radius of the third orbit.

Concept: undefined - undefined
Chapter:
SECTION B - 14 MARKS
[2]2. (i)

Four-point charges Q1 = +17.7 μC, Q2 = −8.85 μC, Q3 = −17.7 μC and Q4 = 35.4 μC are kept as shown in Figure 1 below.

Calculate electric flux emanating from the closed surface S.

Concept: undefined - undefined
Chapter:
OR
[2]2. (ii)
  1. Find the value of current ‘I’ in Figure 2 given below.
  2. State the conservation principle on which your calculation is based.

Concept: undefined - undefined
Chapter:
[2]3.

You are provided with three identical capacitors, each of capacitance “C”.

If Cp is equivalent capacitance when they are connected in parallel and C, isequivalent capacitance when they are connected in series, calculate the ratio `C_s/C_p`.

Concept: undefined - undefined
Chapter:
[1]4. (i) (a)

What is the effect of doubling the current flowing through a metallic wire on drift speed of free electrons?

Concept: undefined - undefined
Chapter:
[1]4. (i) (b)

What is the effect of doubling the current flowing through a metallic wire on relaxation time of free electrons?

Concept: undefined - undefined
Chapter:
OR
[2]4. (ii)

Draw a labelled circuit diagram of a potentiometer used to compare emfs of two given cells X and Y. (Procedure and formula are NOT required.)

Concept: undefined - undefined
Chapter:
[1]5. (i)

Express the Biot-Savart law in vector form.

Concept: undefined - undefined
Chapter:
[1]5. (ii)

State Ampere’s circuital law.

Concept: undefined - undefined
Chapter: [7] Moving Charges and Magnetic Field
[2]6.

A bi-convex lens of focal length f1 is placed in air as shown in Figure 3(a) below. The radii of curvature of its first and second surfaces are R and 2R respectively. The lens is cut along the plane CD. Compare the focal length f2 of the resulting lens shown in Figure 3(b) with that of the original lens shown in Figure 3(a).

Concept: undefined - undefined
Chapter:
[1]7. (i)

Name the electromagnetic wave that scans the contents of the luggage of a traveller during a security check.

Concept: undefined - undefined
Chapter:
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[1]7. (ii)

Which physical quantity is the same for UV rays, red light and radio waves when they are travelling in vacuum?

Concept: undefined - undefined
Chapter:
[2]8.

The work functions for metals M1 and M2 are 1.9 eV and 5.0 eV respectively. Perform necessary calculations to find out which metal emits photoelectrons, when monochromatic light of wavelength 410 nm is incident on them.

Concept: undefined - undefined
Chapter:
SECTION C - 27 MARKS
[3]9.

Show that the intensity of electric field at a point in end on position i.e., axial position of an electric dipole is given by:

`E = (1/(4πε_0))(2pr)/(r^2 - l^2)^2`

where the terms have their usual meaning.

Concept: undefined - undefined
Chapter:
[3]10. (i)

In the circuit shown in Figure 4 below, how much resistance should be connected to a 10 Ω resistor so that the points M and N are at the same potential?

Concept: undefined - undefined
Chapter:
OR
[3]10. (ii)

Figure 5 below shows a battery consisting of three cells. Their emfs and internal resistances are also shown.

Calculate:

  1. emf of the battery.
  2. internal resistance of the battery.
Concept: undefined - undefined
Chapter:
[3]11. (i)

Obtain an expression for magnetic flux density B at the centre of a circular coil of radius R, having N turns and carrying a current I.

Concept: undefined - undefined
Chapter:
OR
[2]11. (ii) (a)

Two moving coil galvanometers G1 and G2 are identical except for the following features:

Features G1 G2
Number of turns 50 60
Area of the coil 30 cm2 40 cm2
Resistance of the coil 4 Ω 6 Ω

Perform calculations to determine which galvanometer has greater current sensitivity.

Concept: undefined - undefined
Chapter:
[1]11. (ii) (b)

In a moving coil galvanometer, how is magnetic field made radial?

Concept: undefined - undefined
Chapter:
[3]12.

Figure 6 below shows a long straight conductor X carrying a current I1. A point P is at a perpendicular distance ‘r1’ from it.

  1. How much force conductor X exerts on a short conductor Y of length ‘l’ which is carrying a current ‘I’ and is kept at point P parallel to the conductor X?
  2. Another long wire Z carrying a current I2 is now kept parallel to X and Y at a distance ‘r2’ from Y such that the conductor Y remains at rest. Obtain the relation between the currents I1 and I2.
Concept: undefined - undefined
Chapter:
[3]13.

A monochromatic ray of light incident on one refracting surface of an equilateral prism, suffers a deviation as shown in the Figure 7 below:

  1. Calculate the refractive index of the material of the prism.
  2. Whats meant by dispersive power of a transparent material?
Concept: undefined - undefined
Chapter:
[3]14.

Draw a ray diagram of Astronomical Telescope for the final image formed at infinity

Concept: undefined - undefined
Chapter:
[3]15.

Kabir and Neha conducted experiments on light as part of their school project. Both of them worked with the same source of monochromatic yellow light. Both obtained patterns on the screen which consisted of alternate bright and dark bands.

The images below depict their results.

  1. Identify the phenomenon observed by Neha.
  2. The teacher asked Kabir to replace monochromatic yellow light with white light. What would be Kabir’s observation now?
  3. What conclusion would be drawn by Kabir and Neha about the nature of light?
Concept: undefined - undefined
Chapter:
[3]16.

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CISCE previous year question papers ISC Class 12 Physics (Theory) with solutions 2025 - 2026

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