Sample Question Paper 2025
Class: XII
Subject: Physics (042)
Maximum Marks: 70
Time Allowed: 3 Hours
General Instructions
- All questions are compulsory.
- The question paper consists of 30 questions divided into four sections A, B, C and D.
- Use of the calculator is not permitted.
- You may use the following values of physical constants wherever necessary:
SECTION – A (6 × 1 = 6 Marks)
(Q.1–6 are 1 mark questions. Each question is compulsory.)
Q1. Name the physical quantity whose SI unit is ohm metre.
Q2. A positively charged particle moves in a uniform magnetic field perpendicular to its velocity. What happens to its kinetic energy?
Q3. State the principle on which a Transformer works.
Q4. Write the expression for the speed of electromagnetic waves in a medium of permeability and permittivity .
Q5. What is the function of a photodiode in solar cells?
Q6. Assertion-Reason Type:
Assertion (A): Photoelectric effect supports the particle nature of light.
Reason (R): The stopping potential depends only on the frequency of incident light and not on its intensity.
Choose the correct option:
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R 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.
SECTION – B (6 × 2 = 12 Marks)
Q7. Draw the V–I characteristics of a p-n junction diode in forward bias. Why does current increase rapidly after threshold voltage?
Q8. Write two differences between conductor and semiconductor on the basis of energy band diagrams.
Q9. Derive an expression for the resistivity of a conductor in terms of relaxation time, number density of electrons and their charge.
Q10. A 10 μF capacitor is charged by a 100 V supply. It is then disconnected from the supply and connected to another uncharged 20 μF capacitor. Find the final potential difference across each capacitor.
Q11. A biconvex lens made of glass (μ = 1.5) has radii of curvature 20 cm each. Calculate its focal length.
Q12. Two cells of emf 2V and 4V are connected in parallel across a resistor of 5 Ω. The internal resistances are 1 Ω and 2 Ω respectively. Find the current through the resistor.
SECTION – C (10 × 3 = 30 Marks)
Q13. Derive the expression for the capacitance of a parallel plate capacitor filled with dielectric medium of dielectric constant K.
Q14. A parallel beam of monochromatic light of wavelength 600 nm falls on a single slit producing a diffraction pattern. The angular width of the central maximum is found to be rad. Calculate the slit width.
Q15. Define the term 'threshold frequency'. Derive an expression for Einstein’s photoelectric equation.
Q16. A circular coil of radius 5 cm and 100 turns carries a current of 3 A. Calculate the magnetic field at its centre.
Q17. (a) Define Half-life of a radioactive element.
(b) The half-life of a radioactive isotope is 10 minutes. What fraction of the original sample will remain after 30 minutes?
Q18. Explain the working of a step-down transformer with the help of a diagram.
Q19. Write the truth table of NAND gate. Prove that NAND is a universal gate.
Q20. Explain the principle of working of AC generator. Draw a labelled diagram.
Q21. A convex lens of focal length 15 cm is placed in contact with a concave lens of focal length 20 cm. Find the effective focal length and power of the combination.
Q22. Draw a labelled ray diagram for the formation of image in a compound microscope. Write the expression for its magnifying power in normal adjustment.
SECTION – D (4 × 5 = 20 Marks)
Q23. Case Study – Communication Systems
Read the following passage and answer the questions:
Communication systems require a source, a channel, and a receiver. Noise plays an important role in determining the efficiency of the system. The range of frequencies used for audio communication is called bandwidth. For example, the AM radio band is from 540 kHz to 1600 kHz, while FM radio uses 88 MHz to 108 MHz.
(a) What is the bandwidth of AM radio?
(b) Which has better sound quality – AM or FM? Why?
(c) Why is skywave propagation used in short-wave bands?
(d) Give two applications of communication satellites.
(e) Mention one source of noise in communication systems.
Q24. Derive the expression for the electric field due to a uniformly charged ring at a point on its axis.
Q25. A compound microscope consists of an objective lens of focal length 2 cm and an eyepiece of focal length 5 cm. The two lenses are separated by 20 cm. The final image is formed at infinity. Calculate the magnifying power of the microscope.
Q26. (a) State and explain the principle of working of a cyclotron. Draw its schematic diagram.
(b) A cyclotron is designed to accelerate protons. If the magnetic field is 1.5 T and the maximum radius of the path is 0.5 m, calculate the kinetic energy (in MeV) of the proton beam obtained.
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