from the surface of a metal depends on the sources such as heat
energy,energy stored in due field,light energy and kinetic energy of
the electric charges bombarding the metal surface.And the four types
of emissions are: 1.Thermionic emission: When a metal is
heated to sufficient temperature,enough thermal energy is imparted to
electrons to enable them to escape from the metal surface.If the
temperature increases electron emission also increases.This method is
known as thermionic emission. 2.Field
emission:When the potential difference between two electrodes is
extremely high,electrons are emitted from the negative electrode,even
at ordinary temperatures.
This process of electron emission is known as field emission.Field
emission does not depend on the temperature of the surface but it is
on the potential difference. 17:37
