Atomic structure: Discharge tube, discovery of cathode rays and properties of cathode rays

Atomic structure: Discharge tube, discovery of cathode rays and properties of cathode rays

Discharge tube

A glass tube containing two electrodes (cathode and anode) connected with high voltage battery and fitted with vacuum pump is called a discharge tube.

Discovery of cathode rays

In the beginning, the electric current was passed through a gas enclosed in a discharged tube at an ordinary pressure and high voltage of 5000 volt, a glow was appeared. When pressure was reduced to 0.001 torr, and voltage was increased from 5000 to 10000 volts, a glow was disappeared. When pressure was further reduced, certain rays were produced from cathode and travel to anode. Such rays are called cathode rays.

These rays are called cathode rays because these rays are produced from cathode surface.

Question: Why discharge tube does not allow the current to pass at ordinary pressure?

Answer.

At ordinary pressure, electrons are not able to overcome the pressure applied on the surface of cathode by gas. However, when pressure is further reduced to 0.01 torr, current starts to pass.

Properties

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