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Shane Macguire Grade: upto college level
        The coil of an electric bulb takes 40 watts to start glowing. If more than 40 W is supplied, 60% of the extra power is converted into light and the remaining into heat. The bulb consumes 100 W at 220 V. Find the percentage drop in the light intensity at a if the supply voltage changes from 220 V to 200 V. 
3 years ago

Answers : (1)

Deepak Patra
askIITians Faculty
474 Points
										xSol. P = 100 w V = 220 v

Case l : Excess power = 100 – 40 = 60 ww
Power converted to light = 60 * 60/100 = 36 w
Case ll : Power = (220)^2/484 = 82.64 w
Excess power = 82.64 – 40 = 42.64 w
Power converted to light = 42.64 * 60/100 = 25.584 w
∆P = 36 – 25.584 = 10.416
Required % = 10.416/36 *100 = 28.93 = 29%
3 years ago
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