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Physics-

General

Easy

Question

Five lumen/watt is the luminous efficiency of a lamp and its luminous intensity is 35 candela. The power of the lamp is

80 W
176 W
88 W
36 W

The correct answer is: 88 W

Efficiency of light source
$eta equals fraction numerator phi over denominator p end fraction$ ..... (i)
and $L equals fraction numerator phi over denominator 4 pi end fraction$ ..... (ii)
From equation (i) and (ii)
$rightwards double arrow p equals fraction numerator 4 pi L over denominator eta end fraction equals fraction numerator 4 pi cross times 35 over denominator 5 end fraction almost equal to 88 W$ .

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