2014

PHYSICS (Theory)

Full Marks: 70

Time: 3 hours

The figures in the margin indicate full marks for the questions

1. Answer the following questions: 1x8=8

- Give the dimensions of Tesla.
- Show that Weber = Volt x Second.
- State Ampere’s circuital law.
- Why are infrared waves called heat waves?
- State Snell’s law of refraction of light.
- Complete the nuclear reaction –

- Write down the truth table of NAND gate.
- Give one use of solar cell.

2. State Coulomb’s law of electrostatics. Explain it in vector form. 1+1=2

Or

What is electric polarization vector? Define the electric susceptibility. 1+1=2

3. State Ohm’s law of current electricity. Define One Ohm resistance. 1+1=2

Or

Find the equivalent resistance between A and D. 2

4. What do you mean by specific resistance of a conductor? What is its S.I. unit? 1+1=2

Or

What is a potentiometer? Would you prefer a voltmeter or a potentiometer to measure the e.m.f of a battery? 1+1=2

5. Explain how Lenz’s law establishes the law of conservation of energy. 2

6. Describe in brief the concept of displacement current. 2

Or

How does a charge ‘q’ oscillating at certain frequency produce electromagnetic waves? 2

7. State two important differences between interference and diffraction. 2

Or

Two lenses of powers + 5D and – 3D are in contact. Find the focal length of the combination. 2

8. Write down Einstein’s photo electric equation and explain each of its terms. 2

Or

Work function of Caesium is 2.14eV.

- Find its threshold frequency.
- If its stopping potential is 0.6V, find the wavelength of the incident radiation.

2

9. Find the wavelength of an electron accelerated through a potential difference of 1 Volt. 2

10. Define 1 Curie unit of radio-activity. What do you mean by ‘half life’? 1+1=2

11. Draw a labeled block diagram of a radio transmitter. 2

12. Apply Gauss’s theorem to calculate the electric field due to an infinite plane sheet of charge. 3

13. Deduce an expression for the capacity of a parallel plate condenser. 3

Or

If, calculate the electric flux through a surface of area 20cm2 in plane. 3

14. Apply Kirchoff’s law of current electricity to establish the condition of a balanced Wheatstone’s bridge. 3

15. Using Ampere’s circuital law, find the magnetic flux density at the centre of a long solenoid carrying current. 3

Or

Describe the working of a moving coil galvanometer. 3

16. Obtain an expression for torque acting on a rectangular coil carrying current placed in a uniform magnetic field. 3

Or

Distinguish among paramagnetic, ferromagnetic and diamagnetic materials qualitatively. 3

17. Deduce the relation for a concave lens. 3

Or

An image is placed 30cm away from a concave lens of focal length 15cm. Find the position, size and nature of the image. 3

18. Find the expression of fringe width for Young’s double slit interference pattern where 2d is the separation between the two coherent sources. 3

Or

Find the value of angle of minimum deviation of a prism [Given]

19. Explain mass defect and binding energy. 3

Or

If, calculate the binding energy of the nitrogen nucleus in. 3

20. What is demodulation? Why is satellite communication necessary for TV signals? 1+1+1=3

Or

What is the basic difference between amplitude modulation and frequency modulation? Discuss the role of ionosphere in radio-wave communication. 1+2=3

21. An inductor of self inductance is connected in series with a non inductive resistor of resistance. A source of e.m.f. Volt is connected in the circuit. Find the 1+2+2=5

- Reactance of the coil.
- Impedance of the circuit.
- Rms voltage drop across the inductor.

Or

Explain briefly with the help of a labeled diagram the basic principle of the working of an a.c. generator. Give two reasons for energy loss in an actual transformer. 3+2=5

22. What are unpolarised and linearly polarised light waves? Establish Brewster’s law. What is the Polaroid? 2+2+1=5

Or

Establish the following relation –

23. Draw a common-emitter amplifier circuit using an n-p-n transistor and explain the amplifier action. Find an expression for a.c. voltage gain. 1+3+1=5

Or

What is photodiode? Explain its working principle. What is a solar cell? 1+3+1=5