State (a) the principle upon which the lightening in fluorescent tubes operate; (b) two factors on which the colour of light from a fluorescent tube depends...
Question 1 Report
State (a) the principle upon which the lightening in fluorescent tubes operate;
(b) two factors on which the colour of light from a fluorescent tube depends.
Answer Details
(a) Principle of operation of a fluorescent tube. When an electric discharge is passed through mercury vapour at low pressure inside the tube, the mercury atoms are excited and emit ultraviolet radiation. This ultraviolet radiation strikes the fluorescent powder (phosphor) coated on the inside wall of the tube, causing it to fluoresce, that is, to absorb the ultraviolet and re-emit the energy as visible light.
(b) Factors on which the colour of the light depends:
- The nature (chemical composition) of the fluorescent powder (phosphor) coating the inside of the tube.
- The type of gas or vapour used in the tube (and its pressure).
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