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As mentioned above, the late nineteenth century scientists conducted several experiments, and found that atoms are divisible. They conducted experiments with gas discharge tubes.

Gas discharge tube

A gas discharge tube is shown in. The gas discharge tube is an evacuated glass tube and has two electrodes, a cathode (negative electrode) and an anode (positive electrode). The electrodes are connected to a high voltage source. Inside the tube, an electric discharge occurs between the electrodes. The discharge or 'rays' originate from the cathode and move toward the anode, and hence are called cathode rays. Using luminescent techniques, the cathode rays are made visible and it was found that these rays are deflected away from negatively charged plates. The scientist J. J. Thompson concluded that the cathode ray consists of negatively charged particles (electrons).

Charge of Electrons

R. A. Millikan conducted the famous oil drop experiments and came to several conclusions: The charge of an electron is –1.602 x 10–19 C. From the charge-to-mass ratio, the mass of an electron was also calculated.

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