Optics Question 499
Question: Two light sources with equal luminous intensity are lying at a distance of 1.2 m from each other. Where should a screen be placed between them such that illuminance on one of its faces is four times that on another face
Options:
A) 0.2 m
B) 0.4 m
C) 0.8 m
D) 1.6 m
Show Answer
Answer:
Correct Answer: C
Solution:
According to the problem $ \frac{I _{A}}{x^{2}}=4\frac{I _{B}}{{{(1.2-x)}^{2}}} $
$ \Rightarrow \frac{1}{x^{2}}=\frac{4}{{{(1.2-x)}^{2}}} $
$ \Rightarrow \frac{1}{x}=\frac{2}{1.2-x} $
$ \Rightarrow x=0.4m $ and $ 1.2-x=0.8m $ .
