Thermionic emission is the emission of electrons from heated metal caused by thermal excitation. A pure tungsten filament must reach 2200°C to emit useful electrons. Factors like temperature, area, and work function affect emission. Thermionic emitters are used in electronics, instrumentation, power systems and energy conversion. Photoelectric emission ejects electrons from metals hit by light, also called the photoelectric effect. It differs from thermionic emission which uses heat rather than light to release electrons.

1. Thermionic & Photoelectric
Emission
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GENERAL PHYSICS
Dr. Jonathan Lalrinmawia

2. Thermionic Emission
Thermionic emission is the emission of electrons from a
heated metal (cathode).
Thermionic = Thermal + ions
A pure tungsten filament must be heated to a temperature
of 2200°C to emit a useful number of electrons.
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GENERAL PHYSICS

3. Thermionic Emission
Factors affecting Thermionic Emission
 temperature of the metal surface
 area of the metal surface
 the work function of the metal
Thermionic emitters are used in
 high-frequency vacuum transistors for electronics
 electron guns for scientific instrumentation
 power electronics
 x-ray generation
 energy converters from high-temperature sources
and solar energy.
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GENERAL PHYSICS

4. Photo-Electric Emission.
When light shines on a metal, electrons can be ejected
from the surface of the metal in a phenomenon known as
the photoelectric effect.
Photoelectric = Photo
+ Electric
This process is also often referred to as photoemission,
and the electrons that are ejected from the metal are
called photoelectrons.
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GENERAL PHYSICS

5. Thermionic Emission Vs Photo-
Electric Emission.
During thermionic emission electrons are emitted from
metal surface by providing heat energy, whereas, during
photoelectric emission electrons are emitted from the
surface of metal when sufficient light energy is received.
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GENERAL PHYSICS