Indiscriminate disposal of used fluorescent electric lamps causes mercury pollution in the environment. Why is mercury used in the manufacture of these lamps?

1. A mercury coating on the inside of the lamp makes the light bright white
2. When the lamp is switched on, the mercury in the lamp causes the emission of ultraviolet radiations
3. When the lamp is switched on, it is the mercury which converts the ultraviolet energy into visible light
4. None of the statements given above is correct about the use of mercury in the manufacture of fluorescent lamps

Explanation

Option (b) is correct

• In fluorescent lamps, mercury vapour emits ultraviolet radiation when electric current passes through it. This ultraviolet radiation strikes the phosphor coating on the inner surface of the tube, which then fluoresces and produces visible light. Mercury does not directly convert ultraviolet radiation into visible light; the phosphor coating performs this function.

Answer: (b) When the lamp is switched on, the mercury in the lamp causes the emission of ultraviolet radiations