Electrons were first observed in cathode ray tubes. These tubes had a very small amount of gas inside and a high voltage is applied to the chathod, cathode rays appeared to travel from cathode and anode. Flourescent screen of the tube is light up.
The force on the rays due to the magnetic field is F=evB and since the rays are bent into curve path, it will experience a centripetal force,
evB=mv²/r
e/m=v/Br
From the velocity selector, Fe=Fm
evB=eE
v=E/B
e/m=E/B²r
At the end, the scientist found out that the ratio e/m is equal to 1.76×10^11C/kg and until today the cathode rays we also called it electrons.
From the oil-drop experiment, the charge of an electron and the mass of an electron is determined which are, e= 1.67×10^-19C and also m= 9.11×10^-31kg.
