Electrons : Cathode rays

Discovery of Electron (Cathode Rays)

At the end of nineteenth century several scientists, e.g., Crookes(1879), Julius Plucker(1889), J.J. Thomson(1896) tried to pass electricity through gases. They found that electricity can be passed through gases only when a high voltage is applied on them at very low pressure. 


These experiments showed the emmision of certain invisible rays from cathode. These rays produced fluorescense on glass and affected a photographic plate.
These rays were named as Cathode rays.
Later, H.A. Lorentz (a Dutch physicist) named these particles as Electrons.

Discharge Tube Experiment


A discharge tube consists of a perfectly leak proof hard glass tube with metal electrodes fused in the walls. The tube is connected to a high efficiency vaccum pump which can evacuate the tube at any pressure. The pressure of the gas is reduced to about 10^-2 - 10^-3 mm and a very high voltage ( 5,000 - 10,000 volts. At this stage, the wall of the discharge tube starts glowing with a faint greenish light.

Later on, it was established that the glow flow of the glass wall of the discharge tube was due to the emmision of  a stream  of rays from the cathode. These rays traveled in a straight line normal to the cathode and bombard on the glass wall an other side of the tube. This bombardment of the rays on the glass wall produce a faint greenish fluorescence which causes the glass tube to glow. These rays were named Cathode rays.

Properties of Cathode rays (Electrons)

1) Cathode rays travel in straight line away from the cathode.

2) Cathode rays posses kinetic energy and an composed of material particles.

3) Cathode rays get deflected towards positive electrode when through an electric field.

4) Cathode rays get deflected from their normal path when passed through a magnetic field.

5) Cathode rays produce ionisation in gas.

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