Discovery of Electron, Proton & Neutron

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Discovery of Electron:

In 1897, J. J. Thomson provided experimental evidence for the existence of sub-atomic particles called electrons in the atoms of all elements. This discovery was made using the cathode ray tube experiment .

He showed that when a high electrical potential was applied to a glass discharge tube at a very low pressure (about 0.001 mm Hg), rays were emitted from the negative electrodeElectrodes are conductors, in the form of wires, rods or plates, through which current enters and leaves the electrolyte. When the current leaves the electrodes it is known as the cathode... More (cathode) and travelled towards the positive electrode (anodeAn anode is an electrode of a polarized electrical device through which conventional current enters the device. It is the positive part of electrolytes where oxidation takes place. More) .

As the rays struck the inner surface of the glass tube opposite the cathode, a bright greenish glow was observed. This glow showed the path taken by the rays and confirmed that they travelled in straight lines.

These rays were found to be deflected by electric and magnetic fields , showing that they carried an electric charge. Since the rays moved from the cathode to the anode and were attracted toward the positive electrode, it was concluded that they carried a negative charge . These negatively charged particles were named electrons , and the rays were called cathode rays (since they