Ham Radio General Class Practice Test

Which element of a triode vacuum tube is used to regulate the flow of electrons between cathode and plate?

1. Control grid

2. Heater

3. Screen Grid

4. Trigger electrode

The correct answer is: Control grid

The control grid is the element of a triode vacuum tube that regulates the flow of electrons between the cathode and the plate. In a triode, the cathode emits electrons when heated, and the control grid, which is positioned between the cathode and the plate, influences the number of electrons that can pass through to the plate. By applying a negative voltage to the control grid relative to the cathode, the flow of electrons can be reduced, which in turn controls the tube's output. This unique ability of the control grid to modulate the electron flow is what allows triodes to function as amplifiers and switches in various electronic applications. Other components like the heater provide the necessary thermal energy for electron emission but do not directly control the flow of electrons. The screen grid, often found in tetrode and pentode tubes, enhances performance but is not responsible for the basic regulation in a triode. The trigger electrode, while relevant in some specific types of tubes, is not a standard feature in triodes and does not govern the electron flow in the same way as the control grid does.