Question

Two pieces one of germanium and the other of aluminium are cooled from $T_{1}K$ to $T_{2}K$. The resistance of

• A. aluminium increases and that of germanium decreases.
• B. each of them decreases.
• C. aluminium decreases and that of germanium increases.
• D. each of them increases.

Answer 1

Answer: (C)

aluminium decreases and that of germanium increases.

Here, aluminium is a conductor (metal) while germanium is a semiconductor. Conductors have positive temperature coefficient of resistivity while semiconductors have negative temperature coefficient of resistivity. Hence, when both are cooled from some higher temperature, the resistance of aluminium decreases and that of germanium increases.