Which of the following is correct?
(i) A fluorescent lamp, like the ones commonly found in offices, is a discharged tube in which the inner surface is coated with a fluoresecnet material such as zinc sulphide which is also used on `TV` screen.
(ii)The fluorescent tube is filled with ercury vapor at low pressure. Excitation of the `Hg` atoms by electron bombardment cause the emission of light in the green, blue, and ultraviolet `(UV)` regions.
(iii) When the light strike the inner glass wall, most of the `UV` light is abosorbed by the fluorescent material, which then emits a multitude of longer wavelengths that combine to produce white light.
(iv) Fluorescent lamps are more enegry-efficient and, hence, cheaper to operate than tungsten lamp (ordinary light bulbs).

Options

A. `(i),(iv)`
B. `(ii),(iii),(iv)`
C. `(i),(ii),(iii)`
D. `(i),(ii),(iii),(iv)`

Answer

D

Explanation

The generation of fluorescent light involves only the transfer of radiant enegry-very little heat is produced. As a result, a fluorscent lamp is cool to the touch. Heating the filament of a tungsten lamp to `3000^(@)C` produces visible light and much infrared radiation (heat). Thus, a tungsten light bulb is usually too hot to touch after it has been turned on for a few minutes because a substantial fraction of the input enegry is radiated as heat.