Optics Question 105
Question: A small source of light is to be suspended directly above the centre of a circular table of radius R. What should be the height of the light source above the table so that the intensity of light is maximum at the edges of the table compared to any other height of the source
Options:
A) $ \frac{R}{2} $
B) $ \frac{R}{\sqrt{2}} $
C) R
D) $ \sqrt{2}R $
Show Answer
Answer:
Correct Answer: B
Solution:
$ I _{edge}=\frac{L\cos \theta }{(h^{2}+r^{2})}=\frac{Lh}{{{(h^{2}+r^{2})}^{3/2}}} $ .
For maximum extensity $ \frac{dI}{dh}=0 $ .
Applying this condition have get $ h=\frac{r}{\sqrt{2}} $
