Discovery of Electrons:
At ordinary pressure the air inside the Discharge Tude do not conduct electricity even when the electrodes were connected to a source of very high potential of about 5000 volts.
If the pressure inside the tube is reduced and a high voltage of 5000 - 10000 is applied, an electric discharge is produced through the gas producing a uniform glow inside the tube. By reducing the pressure in the tube still further to about 0.01 tor thr original glow disappears. Rays are produced which creates fluorescence on the glass wall opposite to the cathode. These rays are called cathode Rays. Cathode rays are actually negatively charged particles.
Properties of Cathode Rays and Discovery of Electrons:
Cathode rays are negatively charged.
They produce a greenish fluorescence on striking the wall of the glass tube.
Cathode rays cast shadow when a opaque object is placed in the their path. This proves that they travel in a straight line perpendicular to the surface of cathode.
They rays can drive a small paddle wheel placed in their path. This shows that these rays possess momentum.
Cathode rays can produce X-rays when they strike an anode particularly with large atomic mass.
Cathode rays can produce heat when they fall on matter e.g. when cathode rays from a concave cathode are focused on a platinum foil, it begins to glows.
Cathode rays can ionize gases.
These rays can pass through a thin metal foil like aluminum or gold foil. They can cause a chemicl change because they have reducing effect.
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