LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – PHYSICS

CC 10

FIFTH SEMESTER – November 2008

PH 5505 – ELECTRICITY & MAGNETISM

 

 

 

Date : 05-11-08                       Dept. No.                                          Max. : 100 Marks

Time : 9:00 – 12:00

SECTION – A

Answer ALL the questions.                                                                                         (10×2 = 20 Marks)

 

1. Calculate the electric intensity required to just support a water droplet of mass

10^-9 kg having a charge of 4.9 × 10^-12 coulomb.

2. What is meant by dielectric constant of a medium?
3. Define thermoelectric power. What is a thermo – electric diagram?
4. State Faraday’s laws of electrolysis.
5. State Ampere’s circuital law.
6. Calculate the self-inductance of a 1 metre long solenoid of 400 turns and 5 cm diameter.
7. What do you understand by the time constant of a circuit containing inductance and resistance?
8. Why is a choke coil preferred to a resistor in an ac circuit?
9. What is meant by hysteresis?
10. What is Poynting vector? Give its significance.

SECTION – B

Answer any FOUR questions.                                                                                                 (4×7.5 = 30 marks)

11. Derive an expression for the capacity of a parallel plate capacitor. What will be the capacity if the space between the plates is partially filled with a slab of thickness t and dielectric constant ε_r?
12. Explain, with necessary theory, how a Carey-Foster bridge is used to determine the resistance of a coil of wire.
13. Discuss the theory of Helmholtz double coil galvanometer.
14. Discuss the theory of a  parallel resonant circuit. Mention its use.
15. Give an account of Maxwell’s equations. What is the significance of displacement current?

 

SECTION – C

Answer any FOUR questions.                                                                                             (4×12.5 = 50 Marks)

16. State and prove Gauss’s law in electrostatics. Apply it to find the electric intensity inside and outside a uniformly charged sphere.

 

17. (a) Show that  π= TdE/dT and (ii) d/dT (π/T)+(σ_a-σ_b)/T=0                                          (10.5 marks)

(b)   The emf (micro volts) in a thermocouple, one junction of which is at

0˚C is given by E=1788t – 3t² where t is temperature in degree celcius.

Find the neutral temperature.                                                                                (2 marks)

18. (a) Define coefficient of mutual induction between a given pair of coils.

Describe, with necessary theory, a method of finding it experimentally.                         (10.5 marks)

(b)  A straight solenoid has 60 turns per cm in the primary and 300 turns in the secondary .

The area of cross – section of the solenoid is 5cm². Calculate the mutual inductance.                  (2marks)

19. Discuss the theory of oscillatory discharge of a capacitor through an inductance and a resistance.

 

20. Explain clearly dia, para and ferromagnetism.

 

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