Tuesday, May 10, 2011

Discovery of Electron

In the late nineteenth century some physicists were busy in studying the phenomenon of conduction of electricity through gases at low pressure in a discharge tube (A common discharge tube consists of a glass tube with two metal plates sealed at its two ends, and a device for pumping out the air present in the tube). One of these experiments led to the discovery of electrons. When a source of high voltage electricity of the order of 10,000 volts was connected to the electrodes, no electricity flowed between them. If, however, some of the air was removed from the tube, electricity began to flow from one electrode to the other through the air in the partially evacuated discharge tube and the air in the tube gave off yellowish red light. When still more air was evacuated and the pressure was decreased to say nearly10–4 mm of mercury, the light emitted by the air faded and the walls of the glass tube glowed with green fluorescence due to radiation traveling from cathode to anode in straight lines. Since the rays were coming out from the negative electrode, i.e., cathode, these were called Cathode Rays. Soon after the discovery of the cathode rays, their properties were studied by a number of workers, J.Perrin showed the rays to be streams of negatively charged particles.

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