Gas Discharge Tube | Cathode Rays
This is a device used for studying conduction of electricity through gases. The device consists of a long tube with metal electrodes sealed to each end of the tube.
The pressure of gas with the tube can be altered with the vacuum pump connected to the tube.
The potential difference between the electrodes must be high, say about 1000v and the pressure inside a cathode ray tube is reduced to very low pressure ( say -0.01 mm Hg), the gas in the tube breaks into ions i.e they are ionised.
The positive ions move to the cathode while the negative ions and free electrons move to the anode. The positive ions knock off electrons from the metal of the cathode and those electrons stream towards the anode as cathode rays.
Note: These electrons produced at the cathode are called cathode rays.