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DISCOVERY OF ELECTRON BY DISCHARGE TUBE EXPERIMENT

INTRODUCTION

Gases are bad conductors of electricity. However under reduced pressure and at high potential difference gases conduct electric current.

DISCHARGE TUBE

Discharge tube is a glass tube fitted with two electrodes placed opposite to each other. The tube is sealed and contains a vacuum pump. The function of vacuum pump is to reduced or change the pressure inside the tube. The two electrodes are connected to a high voltage battery.

THE EXPERIMENT
	In discharge tube experiment, at low pressure and at very high potential difference, electric current is passed through the gas.
	OBSERVATION
	Under different pressure different observations were noted;
	At 1cm Hg pressure:
	When pressure inside the tube is reduced to 1 cm of Hg, at a potential difference of a few thousand volts causes a spark to pass like a flash of light.
	At 1 mm Hg:
	At 1 mm Hg, the tube is mostly filled with a glow extending from the positive electrode. This is known as "positive column".
	At 0.001 mm Hg:
	At 0.001 m Hg, the glow disappears and the walls of the glass tube begin to glow with a brilliant green light.
	RESULT
	These observations indicate that some radiation or rays are emitted from cathode. These rays are known as "Cathode Rays". See properties of cathode rays here

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