Describe the conduction band and valence band in metals.

On the basis of band theory, distinguish among insulator, semiconductor, and conductor of electricity.

State anyone difference between the energy band diagram of conductors and that of insulators.

The chromium ions doped in the ruby rod:

The band gaps of an insulator, semiconductor and conductor are respectively ${\mathrm{E}}_{{\mathrm{g}}_1,} {\mathrm{E}}_{{\mathrm{g}}_2} \mathrm{and} {\mathrm{E}}_{{\mathrm{g}}_3}$.The relationship between them can be given as: