Optics Question 500

Question: Two lamps of luminous intensity of 8 Cd and 32 Cd respectively are lying at a distance of 1.2 m from each other. Where should a screen be placed between two lamps such that its two faces are equally illuminated due to two sources

Options:

A) 10 cm from 8 Cd lamp

B) 10 cm from 32Cd lamp

C) 40 cm from 8 Cd lamp

D) 40 cm from 32 Cd lamp

Show Answer

Answer:

Correct Answer: C

Solution:

$ I=\frac{L}{r^{2}}\Rightarrow \frac{L _{1}}{L _{2}}=\frac{r _{1}^{2}}{r _{2}^{2}} $

or $ \frac{8}{x^{2}}=\frac{32}{{{(120-x)}^{2}}} $

Solving it we get $ x=40cm $ .



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