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Electron emission

 Electron emission

Introduction

  1. The phenomenon of emission of electrons from the surface of a metal is called electron emission.

  2. Electron emissions are  of following types :

  1. Thermionic emission

  2. Photoelectric emission

  3. Field emission or Cold cathode emission

  4. Secondary emission









Thermionic emission

  1. It is the phenomenon of emission of electrons from the metal surface when heated  suitably.

  2.  The energy required for emission of electrons from the metal surface is being supplied by thermal energy.

  3.  The emitted electrons are called thermal electrons or thermions. 

  4. The number of thermions emitted depends on the temperature of the metal surface.


Photoelectric emission

  1. The phenomenon of emission of electrons from the surface of metal when light radiation of suitable frequency falls on it  is called Photoelectric effect.

  2.  The energy to the free electrons for their emission is being supplied by light Photons.

  3.  The emitted electrons are called photoelectrons.

  4.  The number of photoelectrons  emitted depends on the intensity of incident light.


Field emission or Cold cathode emission

  1. The phenomenon of emission of electrons from a surface of the metal under the application of a strong electric field is called field emission.

  2.  When a very strong electric field about {"font":{"family":"Arial","color":"#000000","size":14},"backgroundColorModified":false,"backgroundColor":"#ffffff","type":"$","id":"1","code":"$10^{8}$","aid":null,"ts":1625396074398,"cs":"kiJfSut08uw5m7WF7bqy2Q==","size":{"width":26,"height":18}}volt /metre is applied to metal, it emits electrons .


Secondary emission

  1. It is the phenomenon  of electrons from the surface of a metal in large numbers when fast moving electrons called primary electrons strike  the metal surface.

2.The electrons emitted are called secondary electrons.



Photoelectric Effect

  1. The phenomenon of emission of electrons from the surface of metals when radiation of suitable frequency falls on them is called Photoelectric effect

  2.  The emitted electrons are called photoelectrons.

  3.  The electric current so produced is called photoelectric current.



By Shivanand Choudhry

Dual Nature of Matter and Radiation

Class 12 Physics

Lecture-03

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