Gas Discharge Tube Experiment | Discovery of Cathode rays

Discharge tube Experiment (William Crooks Experiment)

(Discovery of Electrons / Cathode rays)

Gases are bad conductors of electricity but it is observed that at low pressure they conduct electricity. For this William purpose Crooks developed a discharge tube or cathode ray tube.

The gas discharge tube consists of :

1. Cylindrical glass tube

2. Two metal electrodes

3. It may contain a gas, air or vapours of any substance

4. Vacuum pump ( The gas can be evacuated to any desired pressure with the help of a vacuum pump)

5. High voltage battery (The metallic electrodes inside the glass tube are connected to a high voltage battery)

6. A slit (used to get a sharp beam of radiation)

Working of Discharge tube:

William Crooks observed that when an electric current was passed through the gas at a normal pressure in a discharge tube, The gas remained unaffected even at 5000 volts.
When the pressure inside the gas tube was reduced below 4 torr, a bright glow appeared inside the tube.
But when the pressure inside the tube was reduced to 0.01 torr by removing gas or air by a vacuum pump and a high voltage of 5000-10,000 volts applied, the original glow of gas disappears and current starts to flow through the gas and the light is emitted.

One the modern examples of a discharge tube are the “ Neon sign”

At further pressure reduction inside the discharge tube, the light emission by the gas stops. At this point, some rays were produced from the cathode and moved towards the anode.
Conclusion:
These rays were given the name cathode rays as they are emitted from the cathode and travel towards the anode.