discovery of electron

DISCOVERY OF ELECTRON:

The Electron was discovered by J.J Thomson by conducting a Cathode ray tube experiment.

For the experiment he used Crooke’s tube, which was 60cm long glass tube and had a small tube attached. To this small tube vacuum pump was attached, it also had two metal plates which were connected to battery by wires.

The tube contained gas at atmospheric pressure. when current at high voltage (10,000volts) was passed following observations were made:

1. When current was passed through a gas at 1 atmospheric pressure and at a very high voltage, nothing happened. That is no visible effect was seen inside the tube.
2. Then further the pressure of gas was reduced by pumping the air out, with the help of vacuum pump. The pressure was reduced to 10^-2atm, then on passing current it was seen that whole tube started glowing green.
3. Then further the pressure was reduced to 10^-4It was seen the whole glow vanished, but it was seen that at the end of the tube (anode side) there was a faint green glow observed.

To confirm the faint glow anode was made perforated, and a zinc sulphide screen (fluorescent material) was placed behind it.

When current was passed under same conditions it also started   glowing green. This confirmed that under those conditions some rays were emitted through cathode, and were travelling towards anode. Those rays were called as cathode rays and found to consist of negatively charged particles called electron.