Optics Question 489

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

[CPMT 1992]

Options:

A) 80 W

B) 176 W

C) 88 W

D) 36 W

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Answer:

Correct Answer: C

Solution:

Efficiency of light source $ \eta =\frac{\varphi }{p} $ ….. (i)

and $ L=\frac{\varphi }{4\pi } $ ….. (ii) .

From equation (i) and (ii)

$ \Rightarrow p=\frac{4\pi L}{\eta }=\frac{4\pi \times 35}{5}\approx 88W $ .



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