Q. A strip of copper and another of germanium are cooled from room temperature to 80 K. the resistance of
A) Each of these decreases
B) Copper strip increases and that of germanium decreases
C) Copper strip decreases and that of germanium increases
D) Each of the above increases
Explanation
(c) Germanium is semiconductor, whereas copper is conductor.
For conductors, $R \propto \mathrm{\Delta}t$
For semiconductors,
$R \propto \frac{1}{\mathrm{\Delta}t}$
Hence, when both are cooled, then resistance of copper decreases whereas that of germanium increases.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.