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 $ .



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