Basic Electrical Theory
METHODS OF PRODUCING VOLTAGE (ELECTRICITY)
The electrons that have escaped from the hot cathode form a cloud of negative charges near it
called a space charge. If the plate is maintained positive with respect to the cathode by a battery,
the electrons in the cloud are attracted to it. As long as the potential difference between the
electrodes is maintained, there will be a steady current flow from the cathode to the plate.
The simplest example of a thermionic device is a vacuum tube diode in which the only electrodes
are the cathode and plate, or anode, as shown in Figure 17. The diode can be used to convert
alternating current (AC) flow to a pulsating direct current (DC) flow.
Figure 17 Vacuum Tube Diode