The saturation current in a triode valve can be changed by changing

Options

A. the grid voltage
B. the plate voltage
C. theseparation between the grid and the cathode
D. the temperature of the cathode

Answer

To solve the question regarding how the saturation current in a triode valve can be changed, we need to analyze the factors involved in the operation of a triode valve.

### Step-by-Step Solution:

1. **Understanding the Triode Valve Structure**:
- A triode valve consists of three main components: the cathode (negatively charged), the anode (positively charged), and the grid (which controls the flow of electrons).

2. **Identifying Saturation Current**:
- The saturation current is defined as the maximum current that can flow through the triode when the dynamic plate resistance is infinite. This means that the current is at its maximum and does not change with further increases in plate voltage.

3. **Analyzing the Options**:
- **Option 1: Grid Voltage**: The saturation current does not depend on the grid voltage. Changing the grid voltage affects the control of the current but does not change the saturation current itself.
- **Option 2: Plate Voltage**: Similar to the grid voltage, changing the plate voltage does not affect the saturation current since it is divided by the dynamic plate resistance, which is infinite at saturation.
- **Option 3: Separation Between Grid and Cathode**: Changing the distance between the grid and cathode does not directly affect the saturation current. The saturation current remains unchanged as it is not dependent on this separation.
- **Option 4: Temperature of the Cathode**: Increasing the temperature of the cathode enhances thermionic emission, meaning more electrons are emitted from the cathode. This increase in emitted electrons leads to an increase in the saturation current.

4. **Conclusion**:
- The only factor that can change the saturation current in a triode valve is the **temperature of the cathode**. Therefore, the correct answer is that the saturation current can be changed by changing the temperature of the cathode.

### Final Answer:
The saturation current in a triode valve can be changed by changing the **temperature of the cathode**.