State the expression of the electrical conductivity of the material of a semiconductor in terms of the mobilities of electrons and holes.

What are the causes of electrical conductivity of a semiconductor?

Explain the electrical conductivity of a semiconductor with the help of band theory.

How is it possible to enhance the electrical conductivity to an intrinsic semiconductor?

why does the electrical conductivity of semiconductors increse with rise in temperature?

Write two ways by which the electrical conductivity of a semiconductor can be increased.

What is the effect of doping on electric conductivity of a semiconductor ?

(a) On raising the temperature, electrical conductivity of a metal decreases, while that of a semiconductor increases. Explain. (b) At very low temperature (0K), intrinsic semiconductors behave like insulators but their electrical conductivities increase with rise in temperature. Why?

Using the concept of free electrons in a conductor, derive the expression for the conductivity of a wire in terms of number density and relaxation time. Hence obtain the relation between current density and the applied electric field E.

Using Gauss' law deduce the expression for the electric field due to a uniformly charge spherical conducting shell of radius R at a point (i) outside the shell.