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SS3: PHYSICS - 1ST TERM

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Fluorescence Lamp

The principle of the gas discharge tube is used in fluorescent tubes for lighting and display of signs.

The tube contains mercury or sodium vapor which glows at very low pressure at the passage of cathode rays. The cathode rays cause the emission of ultraviolent rays when they bombard the mercury vapor. The interior of the fluorescent tube is coated with phosphorus, which gives off visible light when hit by ultraviolent rays.

The color of light produced in a fluorescent tube depends on 

  1. Nature of the gas in the tube 
  2. Nature of the coatings in the tube.

Fluorescent tubes are used as display signs and they are more efficient than filament lamps. Neon gases are mostly used in the tubes which always produce an orange or red color.

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