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In 1885, Sir William Crookes carried out a series of investigations about the behavior of metals heated in a vacuum. The experiment of Crookes and others showed that a heated  cathode produced a stream of radiation, which could cause gases at low pressure to glow and which, make other substances emit light too. The radiation emitted from the cathode was given the name 'Cathode rays'.

In 1879, William Crooke passed the electric current through the gas filled at low pressure. Gas at 0.01 mm mercury pressure was filled in 60 cm long glass discharge tube and two electrodes were placed, at both ends of discharge tube. High potential Difference of the 10,000 volts to 30,000 volts was applied across the electrodes then rays were emitted from cathode and collided with the opposite wall. They produced illumination of green color.

These Cathode rays were actually particles that had a negative charged which were further named Electrons.

Properties of Cathode Rays[]

  • Cathode rays are negatively charged.
  • They do not depend on the nature of gas.
  • The size of the cathode rays were not comparable to an atom's size i.e. they are smaller than the atom.