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.

Gas Discharge 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.
Discovery of Cathode rays/electrons in a gas discharge tube

Also, Read!!

Bohr’s Atomic Model

Defects of Bohr’s atomic model

Rutherford’s Atomic model

Planck’s Quantum Theory

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