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
Show Answer
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 $ .
