question_answer 46)

In terms of a hand theory, what is the difference (i) between a conductor and an insulator (ii) between a conductor and a semiconductor  

Answer:

(i) In a conductor, the energy gap between the valence band and the conduction band is very small and electrons easily flow into the conduction band. Thus, it conducts electricity. On the other hand, in an insulator, the energy gap between the top of the valence band and the bottom of the conduction band is so large that enough energy is not available under normal conditions to promote the electrons from valence band to conduction band. The in-between region is called the forbidden zone. (ii) In conductors, the energy gap between the valence band and conduction band is very small and electrons easily flow into the conduction band. Thus, it conducts electricity. On the other hand, in a semi-conductor, the energy gap between the valence band and the conduction band is smaller than in insulators but larger than in conductors. The thermal energy available under ordinary conditions is sufficient to excite some electrons from valence band to conduction band and thus a small amount of current can flow through them.