A) Substances with energy gap of the order of 10 eV are insulators
B) The conductivity of a semiconductor increases with increase in temperature
C) In conductors the valence and conduction bands may overlap
D) The resistivity of a semicdnductor 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 in increase in conductivity. So, choice [b] is correct. [c] In conductors, the conduction band is either partially filled or the conduction band overlaps 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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