Si and Cu are cooled to a temperature of `300 K`, then resistivity

Options

A. for Si increases and for Cu decreases
B. for Cu increases and for Si decreases
C. decreases for both Si and Cu
D. increases for both Si and Cu

Answer

To solve the question regarding the resistivity of silicon (Si) and copper (Cu) when cooled to a temperature of 300 K, we need to analyze how resistivity behaves in metals and semiconductors with respect to temperature changes.

### Step-by-Step Solution:

1. **Understanding Resistivity**:
- Resistivity is a measure of how strongly a material opposes the flow of electric current. It is affected by temperature.

2. **Behavior of Metals (Copper)**:
- For metals like copper, resistivity increases with an increase in temperature. This is due to the increased scattering of conduction electrons as they gain kinetic energy.
- Conversely, when the temperature decreases, the resistivity of metals decreases because there is less thermal agitation, allowing electrons to flow more freely.

3. **Behavior of Semiconductors (Silicon)**:
- For semiconductors like silicon, the behavior is opposite. As temperature increases, resistivity decreases. This is because higher temperatures provide enough energy to electrons to jump from the valence band to the conduction band, increasing the number of charge carriers.
- When the temperature decreases, the resistivity of semiconductors increases because fewer electrons have enough energy to jump to the conduction band.

4. **Cooling to 300 K**:
- In this scenario, both silicon and copper are cooled to a temperature of 300 K.
- For copper (metal), as the temperature decreases, the resistivity will decrease.
- For silicon (semiconductor), as the temperature decreases, the resistivity will increase.

5. **Conclusion**:
- Therefore, at 300 K, the resistivity of copper decreases while the resistivity of silicon increases.

### Final Answer:
- The resistivity of silicon increases, and the resistivity of copper decreases when both are cooled to 300 K.