Because of the space charge in a diode valve,

Options

A. the plate current decreases
B. the plate voltage increase
C. the rate of emission of thermions increases
D. the saturation current increases

Answer

To solve the question regarding the effect of space charge in a diode valve, we can break it down into a series of logical steps:

### Step-by-Step Solution:

1. **Understanding the Components of a Diode Valve**:
- A diode valve consists of two electrodes: the anode (positively charged) and the cathode (negatively charged). The anode attracts electrons emitted from the cathode.

2. **Defining Space Charge**:
- When electrons are emitted from the cathode, they travel towards the anode. However, as these electrons accumulate near the anode, they create a negatively charged region known as the "space charge."

3. **Effect of Space Charge on Electron Flow**:
- The presence of the space charge creates a repulsive force against the electrons emitted from the cathode. This means that some of the electrons emitted will be repelled back towards the cathode instead of reaching the anode.

4. **Impact on Plate Current**:
- The plate current in a diode valve is primarily due to the flow of electrons from the cathode to the anode. Since the space charge repels some of these electrons, fewer electrons will reach the anode, leading to a decrease in the plate current.

5. **Other Factors Unaffected by Space Charge**:
- It is important to note that the space charge does not affect the plate voltage, the rate of emission of thermions, or the saturation current. These parameters remain constant regardless of the space charge.

6. **Conclusion**:
- Therefore, because of the space charge in a diode valve, the correct conclusion is that the plate current decreases.

### Final Answer:
The plate current decreases due to the presence of space charge in a diode valve.

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