Cathode rays are the stream of fast moving electrons. These rays are produced in a discharge tube at a pressure below 0.01 rom of mercury.
Properties of Cathode Rays
( i) Cathode rays are not electromagnetic rays.( ii) Cathode rays are deflected by electric field and magnetic field.( iii) Cathode rays produce heat in metals when they fallon them.( iv) Cathode rays can pass through thin aluminium or gold foils without puncturing them.( v) Cathode rays can produce physical and chemical change.
( vi) Cathode ray travel in straight line with high velocity momentum and energy and cast shadow of objects placed in their path.
( vii) On striking the target of high atomic weight and high melting point, they produce X-rays.
( viii) Cathode rays produce fluorescence and phosphorescence in certain substance and hence affect photographic plate.
( ix) When any charge particle move in a field where magnetic and electric fields are present, without any deviation, then
Magnetic force = Electrostatic force Bev = Ee or v = E / B
( x)
Specific charge of cathode rays means the ratio of charge and mass.
( xi)
Specific charge of electron was determined by J J Thomson using perpendicular magnetic and electric field applied on a beam of electrons, at the same place.
( xii)
Specific charge of electron e / m = E 2 / 2VB 2
where, E = electric field, B = magnetic field and V = potential difference applied across ends of tube.