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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI 600 034
B.Sc.DEGREE EXAMINATION -PHYSICS
FIFTH SEMESTER APRIL 2018
PH 5512- ELECTRICITY AND MAGNETISM
Date: 30-04-2018 Dept. No. Max. 100 Marks
Time: 09:00-12:00
PART-A
Answer ALL Questions: (10x2=20)
1. State Gauss divergence theorem.
2. Define electric polarization. Give its unit.
3. State Kirchoff's laws.
4. What is a thermoelectric diagram? Draw the thermoelectric line of a Cu-Pb couple.
5. A circular coil has a radius of 0.1m and number of turns of 50. Calculate the magnetic induction at a point at the centre of the coil when a current of 0.1 A flows in it.
6. State Lenz's law.
7. If the charge on a capacitor of capacitance 2μF in leaking through a high resistance of 100 megaohms is reduced to half its maximum value, calculate the time of leakage.
8. Show that Imean=2I0π .
9. Define magnetic susceptibility and ii) magnetic permeability.
10. Define Poynting vector.
PART-B
Answer ANY FOUR Questions (4X7.5=30)
11. State Gauss law. Derive it in a dielectric medium.
12. Derive Poisson's equation staring from the differential form of Gauss law.
ii) Establish a relation between electric intensity, electric polarization and electric
displacement.
iii) Obtain the relation between dielectric constant and dielectric susceptibility.
13. Derive an expression for the electrical conductivity of a metal using Drude-Lawrence theory and hence obtain from it ohm's law.
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14. State Ampere's circuital law and use it to calculate the magnetic field inside a long solenoid.
15. What is power factor? Give the expression of the same.
ii) An alternating voltage of 10 volts at 100 Hz is applied to a choke of inductance 5 henry and of resistance 200 ohms. Find the power factor of the coil and the power absorbed.
16. A plane electromagnetic wave is incident normally at the boundary of two non conducting media. Discuss the phenomenon of reflection and refraction.
PART-C
Answer ANY FOURQuestions (4x12.5 50)
17. What is an electric dipole? Derive an expression for the potential and field at any point due to a dipole.
18. Explain with necessary theory how a Carey Foster bridge may be used to compare two nearly equal resistances. Hence show how the specific resistance of the material of the wire can be determined. (10 2.5)
19. Applyingthermodynamical consideration to the working of thermo-couple, obtain the relation between Peltier and Thompson's coefficients.
20. Explain the principle and construction of a moving coil ballistic galvanometer. Derive an expression relating the quantity of charge flowing through it and the throw obtained. Show how to correct the observed throw for damping.
21. Obtain an expression for the growth and decay of charge in a capacitor through a resistance.
22. Give an account of Langevin's theory of diamagnetism.
ii) What is meant by Hysteresis Retentivity and Coercivity.