In case of a Van Graaff generator, the breakdown field of air is

Options

A. `2xx10^(8)Vm^(-1)`
B. `3xx10^(6)Vm^(-1)`
C. `2xx10^(-8)Vm^(-1)`
D. `3xx10^(4)Vm^(-1)`

Answer

To solve the question regarding the breakdown field of air in the context of a Van de Graaff generator, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Breakdown Field:**
- The breakdown field refers to the electric field strength at which an insulating material (in this case, air) becomes conductive. This occurs when the electric field is strong enough to ionize the air molecules.

**Hint:** Remember that breakdown occurs when the electric field exceeds a certain threshold, causing ionization.

2. **Role of Air in a Van de Graaff Generator:**
- In a Van de Graaff generator, charges accumulate on a large metallic sphere. The air surrounding the sphere acts as a dielectric material, which means it can insulate the charges up to a certain voltage.

**Hint:** Think about how dielectrics behave under electric fields and their role in storing charge.

3. **Ionization of Air:**
- As the voltage increases due to the accumulation of charge, there comes a point where the electric field strength becomes sufficient to ionize the air. At this point, air transitions from acting as an insulator to becoming a conductor.

**Hint:** Consider the transition from insulating to conducting states and what causes this change.

4. **Determining the Breakdown Field Value:**
- The breakdown field for air is a known value, which is approximately \(3 \times 10^6\) volts per meter (V/m). This is the threshold at which air can no longer insulate and starts to conduct electricity.

**Hint:** Look for standard values in physics for breakdown fields of common materials, especially air.

5. **Conclusion:**
- Therefore, the breakdown field of air in the context of a Van de Graaff generator is \(3 \times 10^6\) V/m.

**Hint:** Summarize the findings and relate them back to the original question about the breakdown field.

### Final Answer:
The breakdown field of air in the case of a Van de Graaff generator is \(3 \times 10^6\) volts per meter (V/m).