In an insulator, the energy gap between conduction band and valence band is about;

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:

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

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

The chromium ions doped in the ruby rod: