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The electrical domestic tube light gives white fluorescent light because of

  • A.Colision between molecules of filled gas under electric current
  • B.Heavy current
  • C.Vacuum inside the tube
  • D.Falling of ultra violet rays on the white inner coating of the tube

Answer: D

Because ultraviolet light falls on the white coating inside the tube.

The discharge through mercury vapour emits chiefly in the ultraviolet at 254 nm, which is invisible. The phosphor coating absorbs it and re-emits in the visible range - fluorescence - which is why the tube is called fluorescent.

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