Thermionic emission, Electron gun

THERMIONIC
EMISSION

Definition:

The process of emission of electrons from the hot

metal surfaces is called thermionic emission.

Explanation:

 Metals contain a large number of free
electrons. At room temperature electrons cannot escape the metal surface due to
attractive forces of the atomic nucleus.

If the metal is heated to a high temperature, some of the free electrons may
gain sufficient energy to escape the metal surface.

Thermionic emission can also be produced by electrically heating a fine tungsten filament.

 Typical values of the voltage and current used
are 6
V and 0.3 A
respectively

INVESTIGATING
THE PROPERTIES OF ELECTRONS

Electron
Gun:

Electrical device used to produce
electrons by thermionic emission from a tungsten filament heated by 6 V supply.

An
electron gun is used to investigate the

properties of electron beam.