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 .