CLASS XII – PHYSICS
Time allowed : 3 hours
Max. Marks : 70
- All questions are compulsory
- There are 30 questions in total. Questions 1 to 8 carry one mark each, 9 to 18 carry two marks each, 19 to 27 carry 3 marks each and 28 to 30 carry 5 marks each.
- There is no overall choice, but internal choices are provided. You have to attempt only one choice in full.
- Use of calculator is not permitted.
- You may use the logarithm table, if required.
1. What is electrostatic shielding?
2. Identify the carbon resistor whose colour code is green, blue, red and gold.
3. Energy of a charged particle moving in a magnetic field does not change. Why?
4. What is the phase difference between the voltage across inductor and capacitor in a series LCR circuit?
5. Light waves can travel through vacuum, where as sound waves cannot. Why?
6. What are coherent sources?
7. What is the effect on de Broglie wave length when accelerating potential is increased by four times?
8. Define impact parameter.
9. What is the effect of introducing a dielectric slab in between the plates of a capacitor on its capacitance? Is it possible to reduce the capacitance of a capacitor by introducing a dielectric between the plates ? Why?
10. What are the two important properties of the alloy used for making permanent magnets? What is the effect of large hysterisis of the material used for making permanent magnets?
11. What are the possible reasons for the power losses in a transformer?
12. A test charge of 1.6 x 10-19 C is moving with a velocity v = 2i + 3j ms-1 in a magnetic field B = 2i + 3j T. Find the force acting on the test charge.
13. Obtain the resonant frequency and Q – factor of a series LCR circuit with L = 3H, C = 27 µF and R = 7.4Ω.
14. Identify the components of electromagnetic spectrum used for i) sterilizing surgical instruments
ii) detecting cracks in finished metal products
iii) taking photographs through smoke
iv) used in nuclear reactions.
Identify the electromagnetic waves associated with the following wavelengths.
i) 10-3m ii) 10-3nm iii) 500 nm iv) 1m.
15. Distinguish between resolving power and magnifying power of a telescope.
16. The energy levels of an atom are shown. Which transition corresponds to emission of radiation of maximum wavelength?
17. The input waveforms to a gate and the corresponding output are given. Identify the gate and write its truth table.
18. Distinguish between space wave and sky wave.
19. Define drift velocity. From the relation between drift velocity and current deduce Ohm’s law.
Four identical cells each of emf 2V are joined in parallel supplying current to an external circuit consisting of two 15 ohm resistors joined in parallel. The terminal voltage of the cells as read by an ideal voltmeter is 1.6V. Calculate the internal resistance of the cell.
21. Define the magnetic elements of Earth. The horizontal and vertical components of magnetic fields at a place are 0.22T and 0.38 T respectively. Find the resultant intensity and angle of dip at the place.
22. Define self inductance of a coil. Derive an expression for the energy stored in a coil carrying current.
23. With the help of a schematic diagram , explain the working of a reflecting type telescope. What are the advantages of reflecting type telescopes?
What is hypermetropia? Show the defect and its correction using ray diagrams.
24. High precision instruments are using prisms for refection, instead of mirror. Which phenomenon is involved in it?
Polarizing angle of water is 520. Find its critical angle.
25. Draw the graphs showing the variation of photoelectric current with collector potential for i) different intensities and same frequency ii) different frequencies and same intensity of the incident photons.
26. Define mean life. Show mathematically that radioactive decay follows exponential variation.
27. What is the necessity for modulation? In AM wave , which characteristic of the carrier wave is changed?
28. i) Explain the principle, construction and working of a van de Graaff generator.
ii) Draw the equi potential surface for a point charge. OR
i) Derive an expression for the potential at a point due to an electric dipole.
ii) Hence find the expressions for the potential at a point along the
a) axial line b) equitorial line.
29. i) Derive lens maker’s formula.
ii) The radius of curvature of either face of a convex lens is equal to its focal length. What is the refractive index of its material?
i) Derive mirror equation for a concave mirror.
ii) A 4.5cm needle is placed 12cm away from a convex mirror of focal length 15cm. Find out the location of the image and magnification
30. i) With the help of a neat and labeled circuit diagram, explain the working of an n- p-n transistor as an amplifier in common emitter configuration.
ii) Derive expressions for the voltage gain and power gain of the amplifier.
i) What is doping?
ii) Explain the formation of a p-type extrinsic semiconductor.
iii) Draw the energy level diagrams for the p-type and n- type semiconductors.