A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of -

Options

A. each of them increases
B. each of them decreases
C. copper decreases and germanium increases
D. copper increases and germanium decreases

Answer

C

Explanation

We know that resistance of conductor is directly proportional to temperature (i.e `R prop Delta t`), while resistance of semiconductor is inversely proportional to temperature `(i.e. R prop (1)/(Delta t))`.
Therefore, it is clear that resistance of conductor decreases with decrease in temperature of vice-versa, while in case of semiconductor, resistance increases with decrease in temperature of vice-versa.
Since, copper is pure conductor and germanium is a semiconductor hence, due to decrease in temperature, resistance of conductor decreases while that of semiconductor increases.