Ancient scientists had been probing into the structure of matter. Dolton,in 1808 was the first to put forward the structure of matter on scientific lines in the form of his famous dalton's atomic theory.
Cathode rays:
Sir j.j thomson while studying the effect of high voltage current on gases (at low pressure)found that the atom is not the ultimate particle of matter, but consists of still smaller particles.
He took a hard glass cylindrical discharge tube fitted with two metal electrodes.It had a side tube with the help of which air can be exhausted.On passing high voltage current through the which were called cathode rays were found to travel in straight lines in the from of a stream perpendicular to the cathode.& sir.j.j.thomson found that ratio of the charge to mass(e/m) to be the same for all cathode rays irrespective of the nature of gas in the discharge tube and the value of e/m is 1.76*108 coulombs per gram.Millikan found that the charge on each electron is the same i.e., 1.60*10-19 coulomb (one unit negative charge).The mass of an electron is 9.10*10-28 g or 9.10*10-31kg,which is nearly 1/1837th of that of hydrogen.Thus an electron may be defined as a sub-atomic particle which carries one unit negative charge and has a mass nearly equal to 1/1837th of that of hydrogen.
Properties of cathode rays:
1. The cathode rays travel in straight lines at right angles to the surface of cathode.
2. Cathode rays consist of material particles.observation.
3. Cathode rays produce heating effects.
4.They produce greenish flourescene on the walls of the glass tube and also affect the photographic plate.
5.When an electric field is applied on the cathode rays,they are deflected towards the positive plate of the electric field.This shows that cathode rays carry negative charge.
6.Cathode rays bring about ionization of the gases through which they pass.
7.They produce x-rays when they are made to fall on metallic targets such as tungsten,copper etc.
8.They penetrate through thin aluminium foils before being absorbed.