Class 12 Physics Dual Nature Radiation Matter Types of Electron Emission

Types of Electron Emission:

There are 3 types of electron emission; a) thermionic emission, b) field emission, and c) photoelectric emission

  1. Thermionic emission:
  • Thermionic emission is the process in which thermal energy is used to overcome the work function of metal in order to force out the free electrons from the metal surface. It is used in thermionic converter
  • In thermionic converter, comparatively hot electrode emits electrons on receiving thermal energy. These electrons move towards the comparatively cold electrode, thus producing thermionic current (and power).


  1. Field Emission:
  • Field emission is the process where free electrons are forced out of metal surface using a strong electric field ()
  • It is used in field electron microscopes, vacuum nano electronics and other such fields of study.
  1. Photoelectric Emission:
  • Photoelectric emission is the process where free electrons are removed from a metal surface using a light of certain frequency on that metal
  • It is used in image sensor (where optical image is transformed into electric signals), applied mainly in digital cameras.
  • It is also used in gold leaf electroscope,used to detect and measure static electricity.

  • Metal cap, on acquiring some charge passes it to the metal stem and the gold leaf inside the evacuated chamber through the instructor. The gold leaf having the same charge as the metal stem gets repelled and move away as shown in the figure.

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