Electrical conductivies of Ge and Na are `sigma_(1)` and `sigma_(2)` respectively. If these substances are heard, then

Options

A. `sigma_(1)` decreases and `sigma_(2)` increases
B. both `sigma_(1)` and `sigma_(2)` decreases
C. both `sigma_(1)` and `sigma_(2)` increases
D. `sigma_(1)` increases and `sigma_(2)` decreases

Answer

To solve the question regarding the electrical conductivities of germanium (Ge) and sodium (Na) when heated, we can follow these steps:

### Step 1: Understand the materials
- Germanium (Ge) is a semiconductor, while sodium (Na) is a metal and a good conductor of electricity.

### Step 2: Analyze the behavior of conductivities with temperature
- For semiconductors like germanium, the electrical conductivity (σ₁) increases with an increase in temperature. This is because, at higher temperatures, more charge carriers (electrons and holes) are generated, which enhances conductivity.

- For metals like sodium, the electrical conductivity (σ₂) generally decreases with an increase in temperature. This is due to increased lattice vibrations at higher temperatures, which scatter the electrons and reduce their mobility, leading to lower conductivity.

### Step 3: Compare the effects of heating on both materials
- When heated:
- σ₁ (for germanium) increases.
- σ₂ (for sodium) decreases.

### Step 4: Conclusion
- Based on the behavior of electrical conductivities with temperature, we can conclude that:
- The conductivity of germanium increases while the conductivity of sodium decreases when both are heated.

### Final Answer
The correct option is D, which states that the conductivity of germanium increases while that of sodium decreases with an increase in temperature.

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