The plate current in a diode is zero. It is possible that

Options

A. the plate voltage is zero
B. the plate voltage is slightly negative
C. the plate voltage is slightly positive
D. the temperature of the filament is low

Answer

To solve the question regarding the conditions under which the plate current in a diode is zero, we can analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Plate Current**:
The plate current (IP) in a diode is determined by the equation:
\[ I_P = \frac{\Delta V_P}{R_P} \]
where \( \Delta V_P \) is the change in plate voltage and \( R_P \) is the dynamic plate resistance.

2. **Option 1: Plate Voltage is Zero**:
- If the plate voltage \( V_P = 0 \), then:
\[ I_P = \frac{0}{R_P} = 0 \]
- Therefore, this option is **correct**.

3. **Option 2: Plate Voltage is Slightly Negative**:
- A slightly negative plate voltage means that \( V_P \) is close to zero but negative. For example, if \( V_P = -0.0001 \) V, then:
\[ I_P = \frac{-0.0001}{R_P} \approx 0 \]
- Since this value is very small, we can conclude that this option is also **correct**.

4. **Option 3: Plate Voltage is Slightly Positive**:
- Similarly, if the plate voltage is slightly positive (e.g., \( V_P = 0.0001 \) V), then:
\[ I_P = \frac{0.0001}{R_P} \approx 0 \]
- Thus, this option is also **correct**.

5. **Option 4: Temperature of the Filament is Low**:
- The filament (cathode) needs to be heated sufficiently to emit thermions (electrons). If the temperature is low, thermionic emission does not occur, resulting in no current flow:
- Therefore, if the temperature is low, \( I_P = 0 \), making this option **correct** as well.

### Conclusion:
All four options are valid conditions under which the plate current in a diode can be zero.