Question

When electric current flows in a purely resistive circuit electrical energy gets fully converted into heat energy. The amount of heat produced (H) in the circuit is found to be directly proportional to (i) the square of current (I²) (ii) the resistance (R) of the conductor and (iii) the time (t) for which current flows. In other words H = I²Rt. Electrical devices such as an electric fuse, electric heater, electric iron etc. are all based on this effect called heating effect of electric current.

Explain the following.

What are the essential requirements of a heater filament?

A material used for making heating elements of electrical heating devices should have :

Why is the tungsten used exclusively as filament for almost all electric lamps?