Concept:Cathode rays are streams of electrons discovered using discharge tube experiments.
Explanation:Step 1: In a discharge tube, a high voltage is applied across a gas at low pressure.
This produces invisible rays travelling from the cathode to the anode.
These rays were named cathode rays because they originated from the cathode.
Step 2: J.J. Thomson performed the discharge tube experiment in 1897.
He showed that cathode rays consist of negatively charged particles.
He measured their charge-to-mass ratio, proving they were much smaller than atoms.
These particles are now called electrons (
e−).
Step 3: Robert Millikan later measured the exact charge of the electron.
Ernest Rutherford and Niels Bohr contributed to atomic structure, not the discovery of cathode rays.
Therefore, the scientist credited with discovering cathode rays as sub-atomic particles is J.J. Thomson.
Answer:A. J.J Thomson