Hot Cathode, Thermionic Emission

A hot cathode is another way of producing free electrons in contrast to what happens in a discharge tube when electrons are produced from a cold cathode.

Whenever metal is heated to a sufficiently high temperature, electrons are emitted from the surface of the metal.

Thermionic Emission:

Thermionic emission is the giving off or emission of electrons from the surface of a metal when they are heated to a sufficiently high temperature.

When the tungsten filament is heated to a high temperature, the extra energyEnergy is the ability to do work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, and electrical energy. Units of Energy: The SI unit... More is given to its free electron at the surface of the metal which enables it to break through the surface of the metal and exist outside it as an electric cloud. This is the process of thermionic emission and the emitting filament is the hot cathode.

When plate A is positive with respect to hot cathode it attracts the free electrons of the electron cloud and current flows as shown but when negative, it repels the electrons and no current flows.

Thermionic Devices:

Thermionic devices are devices that