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 $ .
