Cathode Rays Experiment and Discovery of Electrons - Home of Knowledge

Cathode Rays Experiment and Discovery of Electrons

CATHODE RAYS EXPERIMENT: In 1895, Sir William Crooks performed experiments by passing electric current through gases in a discharge tube at a very low pressure. During this experiment crooks observed radiations , that were later named electrons.

J.J. Thomson performed a large number of experiments and finally prove that electrons are basic particles of atom that are negatively charged and are responsible for all the chemical properties of the atom. So electrons are proved to be the fundamental particles of an atom.

CONSTRUCTION OF APPARATUS : An apparatus consisted of a glass tube fitted with two metallic electrodes which were connected to the high Voltage battery. The pressure inside the tube was kept at 10-4 atm.

When high voltage current was passed through the gas, shiny rays were emitted from the cathode towards the anode. These rays were given the name of Cathode rays as they were originated from cathode.


CHARACTERISTICS OR PROPERTIES OF CATHODE RAYS : The Properties of cathode rays are as follows.

1)These rays travel in a straight line perpendicular to the cathode surface. 2)They can form a sharp shadow of an opaque object if placed in their path, which proved their particle nature.

3)These are deflected towards positive plate in an electric field showing that they are negatively charged. 4)They raised the temperature of a body on which they fall.

5) J-J Thomson discovered their charge/mass (e/m) ratio. 6)Light is produced when these rays hit the sides of a discharge tube. 7)It was found that the same type of rays were emitted no matter which cathode was used in the discharge tube.

All the above properties suggest that the nature of cathode rays was independent of the nature of gas present in the discharge tube or material of cathode. They produce sharp shadow of an object placed in their path which proved that these are fast moving material particles and are named electrons, which are fundamental particles of all atoms.

For your information: Sir William Crooks(1832-1919) was a British chemist and physicist. He was pioneer of vacuum tubes. He worked on spectroscopy.


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