A point source of light S is placed in front of a perfectly reflecting mirror as shown in Figure. `Sigma` is a screen. The intensity at the center of screen is found to be I.
If the mirror is removed, then the intensity at the center of screen would be

Options

A. `I`
B. `10I//9`
C. `9I//10`
D. `2I`

Answer

c.

Explanation

Let poewr of light source be P, then intensity at any point on the screen it due to light rays directly received from source and that due to lilght rays after reflection from the mirror.
`I=(P)/(4pia^(2))+(P)/(4pixx(3a)^(2))`
When mirror is taken away,
`I_(1)=(P)/(4pia^(2))=(9I)/(10)`