The energy gap between valence band and conduction band in insulators is

The energy gap between valence band and conduction band in insulators is

Right Answer is:

5 eV

SOLUTION

Insulators

  • In an insulator, the valance band is completely filled and there is a large forbidden gap Eg between the valence band and the conduction band. The gap is generally between 5eV to 10 eV. 
  • Under an applied electric field the valence electrons cannot gain enough energy to jump to the conduction band. Further, the exclusion principle does not permit any transition within the valence band. Therefore, no current can flow.
  • Note that the forbidden gap is so large that the electrons cannot go from the valence band to the conduction band by thermal excitation. At room temperature, the thermal energy kT is negligible as compared to the forbidden gap.

The resistivity of insulators lies between 103 to 1017 Ωm at room temperature.

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