1. Derive the expression for the power dissipated per cubic metre per second in a conductor carrying a current density J as a result of an applied electric field E.

2. What is superconductivity Draw· the curve of resistivity vs temperature for normal metal and pure superconductor. Discuss the effect of the magnetic field on superconductor.

3. show that a semiconductor has a minimum conductivity at a given temperature where

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and find the minimum value of conductivity. Also find the minimum conductivity for germanium at a temperature given that ni 2·5 x Mc 0·38 and Mn =0·19

4. Name the conducting materials used in making the following (Give reasons for your answer)

Overhead transmission line

Starter elements used in starting d.c. motors

Heating elements of irons

Brushes for electrical machines

5. What is meant by dielectric strength? With the help of a neat sketch of the apparatus used for testing of transformer oil, explain the method of determining the dielectric strength of the transformer oil.

6. Define the term 'Polarisation'. Discuss ionic and electronic polarisation. Also draw the curve showing the dependency of polarizability on the frequency of the applied alternating electric field.

What are domains in ferromagnetic materials

Give an account of the origin of permanent magnetic dipoles in matter.

8. Write short notes on the following:

Various important properties of insulating materials

Dielectric breakdown mechanism in gases