Why the brightness of light emitted by a bulb decreases gradually with its period of use?
Text Solution
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When the bulb is used, the evaporation of the metal from the filament of bulb takes palce with time which deposits on the inner side of the glass wall as black substance. Due to it, the filament of the bulb becomes thinner and thinner with use. This in turn increases the resistance of the. (`:' R prop 1// pi r^(2)`). As `P = V^(2)//R`, so brightness of bulb decreases gradually with its period of use.
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