🧪 CBSE Class 12 Physics

Sample Question Paper (Academic Session 2025–26)

Time Allowed: 3 Hours
Maximum Marks: 70

General Instructions

All questions are compulsory unless stated otherwise.
The use of calculators is not permitted.
Draw neat and properly labeled diagrams wherever required.
Assume suitable data, if necessary, and justify your assumptions.
Use standard symbols, conventions, and SI units in all answers.
Figures are not to scale unless stated otherwise.

Section A – Very Short Answer (1 × 20 = 20 marks)

Answer all questions. Each question carries 1 mark.

Define electric flux.
Write the SI unit of magnetic flux.
What is meant by the work function of a metal?
State Ohm’s law.
What is the principle of a transformer?
Define the refractive index of a medium.
Write the formula for the de Broglie wavelength.
Define the half-life of a radioactive substance.
What is displacement current?
State one use of optical fibre.
What is meant by binding energy per nucleon?
Define threshold frequency in the photoelectric effect.
What is polarization of light?
State Faraday’s law of electromagnetic induction.
What is meant by a p–n junction?
What is an equipotential surface?
Write the relation between the frequency and wavelength of light.
Define mutual inductance.
What is meant by carrier mobility in semiconductors?
State one use of a Zener diode.

Section B – Short Answer (2 × 8 = 16 marks)

Answer all questions. Each question carries 2 marks.

Derive the relation between electric field and electric potential.
A wire of resistance (R) is stretched to double its length. What will be its new resistance?
Explain the concept of self-inductance with a suitable expression.
Distinguish between diamagnetic and paramagnetic materials (any two points).
State two important properties of electromagnetic waves.
Why is a concave mirror used in vehicle headlights?
What is meant by drift velocity? Write its relation with current.
Explain why sky waves are not used for very high-frequency communication.

Section C – Short Answer (3 × 8 = 24 marks)

Answer all questions. Each question carries 3 marks.

Using Gauss’s law, derive the expression for the electric field due to an infinitely long straight charged wire.
Explain the working of a moving coil galvanometer with a neat, labeled diagram.
Derive the lens maker’s formula for a thin lens in air.
Explain the photoelectric effect and draw the graph between stopping potential and frequency.
Describe the Bohr model of the hydrogen atom and state its limitations.
Explain the construction and working of a full-wave rectifier with waveform.
Derive an expression for the energy stored in a charged capacitor.
Explain nuclear fission with one suitable example.

Section D – Long Answer (5 × 2 = 10 marks)

Answer any two questions. Each question carries 5 marks.

Derive the expression for the magnetic field at the center of a circular current loop using the Biot–Savart law.
Explain Young’s double-slit experiment and derive the expression for fringe width. State the conditions for sustained interference.
Describe the construction and working of a transistor as an amplifier in the common-emitter configuration. Draw the circuit diagram.

Section E – Case Study (5 marks)

Read the passage carefully and answer the questions that follow.

A student performs an experiment to study the V–I characteristics of a p–n junction diode. He observes that the current remains very small in forward bias up to a certain voltage, after which it increases rapidly. In reverse bias, only a very small current flows until breakdown occurs.

(a) What is the forward voltage after which the current rises rapidly called? (1)
(b) Explain why the current increases sharply beyond this voltage. (2)
(c) What is reverse breakdown in a diode? (1)
(d) Draw the V–I characteristics of a p–n junction diode and mark the important regions. (1)

End of Question Paper

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