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(C) When a small amount of impurity atoms are added to a semiconductor,its resistivity generally decreases.Explanation:The conductivity $\sigma$ of a

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decreases.

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(C) When a small amount of impurity atoms are added to a semiconductor,its resistivity generally decreases.Explanation:The conductivity $\sigma$ of a semiconductor is given by $\sigma = n_{e} e \mu_{e} + n_{h} e \mu_{h}$,where $n_e$ and $n_h$ are the number of electrons and holes per unit volume,and $\mu_{e}$ and $\mu_{h}$ are the mobilities of electrons and holes.When impurity atoms are added (doping),the concentration of charge carriers ($n_e$ or $n_h$) increases significantly.Since conductivity $\sigma$ is directly proportional to the carrier concentration,the conductivity increases.As resistivity $\rho$ is the reciprocal of conductivity $(\rho = 1/\sigma)$,an increase in conductivity leads to a decrease in resistivity.

When a small amount of impurity atoms are added to a semiconductor,then generally its resistivity

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