Question

Distinguish between conductor, insulator and semiconductor.

Answer 1

		Conductors	Insulators	Semiconductors
i.	Definition	A substance which conducts heat and electricity to a greater extent is called conductor	A substance which cannot conduct heat and electricity under any conditions is called insulator.	A substance which has poor electrical conductance at low temperature, but higher conductance at higher temperature is called semiconductor.
ii.	Band theory	The energy gap is either very small or there is overlapping between valence band and conduction band.	The energy gap between the valence band and the conduction band is very large.	The energy gap between valence band and conduction band is small.
iii.	Electric conductivity	Under an applied electric field, the electrons can jump from valence band to conduction band and thus, the substance shows conductivity. eg. Cu, Zn, Al, etc.	Under an applied electric field, the electrons cannot jump from valence band to conduction band and hence, such a substance has very small conductivity and behaves as an insulator. eg. Rubber, plastic, etc.	The electrons from valence band can be excited to conduction band on slight heating. The number of electrons that can conduct electricity is lower in semiconductors than in metals. eg. Silicon, germanium, etc.