First slide

Classification of Metals, semiconductors and insulators

Question

Choose the false statement from the following:

Moderate

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 semiconductor increases with increase in temperature.

Solution

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 (1) is correct.
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 (2) is correct.
In conductors, the conduction band is either partially filled or the conduction band overlaps on the valence band. So, choice (3) is correct.
In semiconductor, resistivity decreases with increase in temperature. So, choice (4) is wrong.

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