(1) It was discovered by J.J. Thomson (1897) and is negatively charged particle. Electron is a component particle of cathode rays.
(2) Cathode rays were discovered by William Crooke's & J.J. Thomson (1880) using a cylindrical hard glass tube fitted with two metallic electrodes. The tube has a side tube with a stop cock. This tube was known as discharge tube. They passed electricity (10,000V) through a discharge tube at very low pressure ( 10-2 to 10-3 mm Hg). Blue rays were emerged from the cathode. These rays were termed as Cathode rays.
Properties of Cathode rays
(i) Cathode rays travel in straight line.
(ii) Cathode rays produce mechanical effect, as they can rotate the wheel placed in their path.
(iii) Cathode rays consist of negatively charged particles known as electron.
(iv) Cathode rays travel with high speed approaching that of light (ranging between 10-9 to 10-11 cm/sec)
(v) Cathode rays can cause fluorescence.
(vi) Cathode rays heat the object on which they fall due to transfer of kinetic energy to the object.
(vii) When cathode rays fall on solids such as cu,X-rays are produced.
(viii) Cathode rays possess ionizing power i.e., they ionize the gas through which they pass.
(ix) The cathode rays produce scintillation on the photographic plates.
(x) They can penetrate through thin metallic sheets.
(xi) The nature of these rays does not depend upon the nature of gas or the cathode material used in discharge tube.
(xii) The e/m (charge to mass ratio) for cathode rays was found to be the same as that for an e- (-1.76×108) coloumb per gm). Thus, the cathode rays are a stream of electrons.
(xiii) According to Einstein’s theory of relativity, mass of electron in motion is,
m' = Rest mass of electoron (m)/√[1-(u/c)2]
Where u = velocity of electron, c= velocity of light.
When u = c than mass of moving electron = ∞.