A piece of copper and a piece of germanium are cooled from room temperature to 80K. Then, which one of the following is correct?

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Resistance of each will increase

Resistance of each will decrease

Resistance of copper will decrease with that of germanium will increase

Resistance of copper will increase with that of germanium will decrease

answer is C.

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Detailed Solution

Concept: The temperature of copper metal decreases when a piece of copper is cooled from room temperature (298 K) to 80 K. The resistivity and thus resistance of a metal decreases as its temperature decreases. As a result, when copper pieces are cooled to 80 K, their resistance decreases.
The temperature of a germanium semiconductor is reduced when a piece of germanium is cooled from room temperature (298 K) to 80 K. The resistivity and thus resistance of a semiconducting material increases as the temperature of the material decreases. As a result, when germanium pieces are cooled to 80 K, their resistance increases.
When both copper and germanium are cooled to 80 K, their resistances decrease and increase, respect.
Hence, the correct option is 3.

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