A piece of copper and another of germanium are cooled from room temperature to `80 K`. The resistance of

Options

A. each of them increases
B. each of them decreases
C. copper increases and germanium decreases
D. copper decreases ad germanium increases

Explanation

To solve the problem, we need to analyze the behavior of the resistance of copper and germanium when cooled from room temperature to 80 K.

### Step-by-Step Solution:

1. **Identify the Initial Conditions**:
- Room temperature is approximately 27°C, which is equivalent to 300 K.
- The final temperature after cooling is 80 K.

2. **Understand the Materials**:
- Copper is a good conductor of electricity.
- Germanium is a semiconductor.

3. **Effect of Temperature on Conductors**:
- For conductors like copper, as the temperature decreases, the conductivity increases. This means that the resistivity (ρ) decreases.
- The relationship between resistance (R), resistivity, length (L), and area (A) is given by the formula:
\[ R = \frac{\rho L}{A} \]
- If resistivity decreases, the resistance of copper will also decrease.

4. **Effect of Temperature on Semiconductors**:
- For semiconductors like germanium, as the temperature decreases, the conductivity decreases. This means that the resistivity increases.
- Consequently, the resistance of germanium will increase.

5. **Conclusion**:
- As the temperature is lowered from room temperature to 80 K:
- The resistance of copper **decreases**.
- The resistance of germanium **increases**.

Thus, the answer is:
- The resistance of copper decreases and the resistance of germanium increases.