Class 12 Physics, Chapter 11 Dual Nature of radiation Class12 Physics,Chapter11 Dual Nature of radiation | Page 3

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( xii ) The value of specific charge of an electron is 1.7589 * 10 11 C / kg . ( xiv ) Millikan measured the charge of an electron through his popular oil drop experiment .
( xv ) The charge of the electron as determined by Millikan was found to be 1.602 * 10 -19 C .
Positive Rays
Positive rays were discovered by Goldstein . Positive rays are moving positive ions of gas filled in the discharge tube . The mass of these particles is nearly equal to the mass of the atoms of gas .
( i ) These consist of fast moving positively charged particles . ( ii ) These rays are deflected in magnetic and electric fields . ( iii ) These rays travel in straight line . ( iv ) Speed of positive rays is less than that of cathode rays . ( v ) These rays can produce fluorescence and phosphorescence .
Electron Emission
It is the phenomenon of emission of electron from the surface of a metal . The electron emission can be obtained from the following process
( i ) Thermionic ( ii ) Photoelectric emission ( iii ) Field emission ( iv ) Secondary emission
Photon
Photons are the packets of energy emitted by a source of radiation . The energy of each photon is ,
E = hv Where h is Planck ’ s constant and v is frequency of radiation . The rest mass of a photon is zero . The momentum of a photon p = hv / c = h / λ