| 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. |
| 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. |
