Question

A strip of copper and another germanium are cooled from room temperature to 80 K. Theresistance 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 these increases.

Answer 1

Answer: (C)

copper strip decreases and that of germanium increases

Copper is a conductor of electricity, which conducts when by drifting of electron. Due to fall of temperature randomness of electron flow decreases so, resistance of copper decreases.

Germanium is a semiconductor whose conduction capability depends on number of electrons in conduction band. Cooling leads to decrease in number of conduction electrons. So, resistance increases.

i.e. The temperature coefficient of resistance of copper is positive and that of germanium isnegative, therefore when copper and germanium are cooled, resistance of copper stripdecreases and that of germanium increases.