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 of germanium increases
D. copper increases and of germanium decreases

Answer

To solve the problem, we need to analyze the behavior of the resistance of copper (a conductor) and germanium (a semiconductor) as they are cooled from room temperature to 77 K.

### Step-by-Step Solution:

1. **Understanding Resistance in Conductors**:
- For conductors like copper, the resistance increases with a decrease in temperature. This is because the atoms in the conductor vibrate less at lower temperatures, leading to fewer collisions between electrons and atoms, but the overall resistance still increases due to the reduced thermal energy.

2. **Understanding Resistance in Semiconductors**:
- For semiconductors like germanium, the resistance behaves differently. As the temperature decreases, the number of charge carriers (electrons and holes) available for conduction decreases. This results in an increase in resistance as the temperature drops.

3. **Applying the Concepts**:
- As we cool copper from room temperature to 77 K, we expect the resistance of copper to **increase**.
- As we cool germanium from room temperature to 77 K, we expect the resistance of germanium to **increase** as well.

4. **Conclusion**:
- Therefore, the correct answer is that the resistance of copper increases and the resistance of germanium also increases. However, since the question asks for the behavior of each material, we can summarize:
- Copper: Resistance increases
- Germanium: Resistance increases
- This leads us to conclude that the correct option is **none of the provided options** directly match this conclusion, but if we consider the context of the question, we can infer that the behavior of both materials is increasing.

### Final Answer:
The resistance of copper increases and the resistance of germanium increases.

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