Theory:

Crookes Experiment:
In 1878William Crookes discovered visible rays travelling between two metal electrodes when experimenting with a discharge tube. These rays are called Crookes rays or Cathode rays.
Crookes tube is more commonly known as Cathode Ray Tube (CRT).
  • A long glass tube filled with gas and sealed at both ends is known as a cathode ray tube.
  • It is constructed of two metal plates (which serve as electrodes) connected by a high-voltage wire.
  • The cathode is the electrode that is attached to the battery's negative terminal (negative electrode).
  • The anode is the electrode that is attached to the positive terminal (positive electrode).
  • There is a side tube with a pump attached to it. The pump reduces the discharge tube pressure.
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Cathode Ray Tube
  
Cathode Ray Tube:
  
Electrical discharge:
As electricity travels through air, it extracts electrons from gaseous atoms, resulting in cations' formation. This is known as an electrical discharge.
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Electrical discharge