2 | P a g e
( 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