Thompson's cathode ray tube experiment established the charge-to-mass ratio (m/q) of the electron, which was significantly smaller than that of charged ions in a chemical solution. Direct measurement of a single electron's charge was impractical due to the experimental limitations of the time, particularly before Millikan's oil drop experiment, which quantified the charge of an electron. The challenges included the difficulty in isolating a single electron and accurately measuring the charge deposited on the anode. The m/q ratio was easier to determine as it relied on macroscopic measurements of radius, voltage, and magnetic fields.
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Pranav Jha said:Why couldn't Thompson just let one electron fly across the gap before disconnecting the battery and turning off the beam, and then measure the amount of charge deposited on the anode,thus allowing him to measure the charge of a single electron directly?