William Crookes, in 1870, discovered that on applying a strong electric field between cathode and anode (kept under discharge tube at low pressures), some rays were emitted by the cathode. These rays were noticed as a bright fluorescent on the glass adjacent to the cathode
These rays were called as cathode rays by William Crookes
In 1879, he proposed that these cathode rays are a bunch of fast moving negatively charged particles
Then, J. Thomson (1856-1940) validated the above hypothesis. He found that when ultraviolet radiation falls on a metal surface (or when metal surface is heated), few negatively charged particles are released by the metal surface.
He used electric and magnetic fields (across the discharge tube), mutually perpendicular to each other and the emitted electrons
He was the first to find the values of; speed(v), and the charge to mass ratio (e/m) of the cathode ray particles, experimentally
He found the speed of particles to be about 0.1 to 0.2 times the speed of light (), and the charge to mass ratio (e/m)
He also found that the e/m ratio to be constant, irrespective of the material used as an emitter. This proved the universal nature of cathode ray particles.
In 1897, he termed this negatively charged cathode ray particles as electron, and this name was used for the first time.
A. MIlikan, in 1913 performed experiments to calculate the charge on an oil drop (popularly known as Milikan’s oil drop experiment)
He observed that, every time the charge came to be an integral(whole number) multiple of a small charge (), which is actually the charge on an electron
MIlikan concluded that charge on a matter is quantized (discrete)