ELECTRON EMISSION

• The escaping of electron from metal surface is called electron emission.
• For electron emission electron require sufficient energy.
• The minimum energy required to escape electron from the metal is called the work function of that      metal.
• Work function of different metal is different because the force acting between electrons and proton of different atoms are different.
• Work function is denoted by  phi (Φ).
• Work function of some metals are given below:-

Metal Work function     Cs 2.14 K 2.30 Na 2.75 Ca 3.20 Mo 4.17 Pb 4.25

Metal Work function     Al 4.28 Hg  4.49 Cu 4.65 Ag 4.70 Ni 5.15 Pt 5.65

• Electron emission takes place by following three physical process:-

1.  Thermionic emission:- the emission of electron from the metal surface due to heat energy is called thermionic emission.
2. Field emission:- the emission of electron from metal surface due to strong electric field is known as field emission.
3.  Photo-electric emission:- the emission of electron from metal surface due to the electromagnetic wave fallings on the metal is called  Photo-electric emission.