Monday, 27 May 2013

Conductors, Semiconductors, Insulators

Solids can be classified on the basis of electrical conductivity as:
1) Conductors
2) Semiconductors
3) Insulators

Conductors: The Substances which easily allow electric current pass through them are called conductors. E.g. Copper, Aluminium has large no. of free electrons.

Conductors contain no forbidden energy gap between valance band and conduction band. They overlap each other as shown in the given image. Without supplying any additional energy valance electrons become free electrons which make metals like Copper, Aluminium good conductors of electricity.

Semiconductors: Substance like Germanium, Silicon, Carbon etc. whose electrical conductivity lies between conductor and insulators is called Semiconductors.

These types of materials have almost fully filled valance band and almost empty conduction band. The forbidden energy gap between valance and conduction band is very low and is near about 1.2 eV for Silicon and about 0.72 eV for Germanium.

Heat at room temperature is sufficient to jump electrons from valance band to conduction band which makes them conductive at room temperature.

Insulators: Substances like wood, plastic, glass etc. which do not allow electric current to pass through them are called Insulators.

Insulators have a very high forbidden energy gap between conduction band and valance band which is approximately 5 eV or more. It is impossible to jump the electrons from valance band to conduction band at room temp. This is the reason why insulators do not conduct at room temp.

Good Insulators offer high resistance and low conductivity (almost zero) to the flow of electricity.

No comments:

Post a Comment