A) Substances with energy gap of the order of 10 eV are insulators
B) The conductivity of a semiconductor increases with increases in temperature
C) In conductors the valence and conduction bands may overlap
D) The resistive of a semiconductor increases with increase in temperature
Correct Answer: D
Solution :
(a) In insulators energy gap is of the order of 5 to 10 eV and it is practically impossible to impart this much amount of energy to the electrons in valence band. So, as to jump to conduction band. So, choice (a) is correct. (b) In semiconductors with the rise in temperature more electrons from valence band jump to conduction band and this results is increase in conductivity. So, choice (b) is correct. (c) In conductors, the conduction band is either partially filled or the conduction band overlaps on the valence band. So, choice (c) is correct. (d) In semiconductor, resistivity decreases with increase in temperature. So, choice (d) is wrong.
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