Geometrical OpticsHard
Question
The intensity of light from a source decreases with the distance x from the source, as 
picture, the intensity of light from the source S at point A on a curtain is 8.1 U, where U is some unit. Then we add a big mirror parallel to the curtain at point B. The distances AS and SB are equal, and the points A, S and B are in line, perpendicular to the curtain and the mirror. What is the intensity in U of light reaching point A now ?
picture, the intensity of light from the source S at point A on a curtain is 8.1 U, where U is some unit. Then we add a big mirror parallel to the curtain at point B. The distances AS and SB are equal, and the points A, S and B are in line, perpendicular to the curtain and the mirror. What is the intensity in U of light reaching point A now ?Options
A.9
B.15
C.12
D.18
Solution
Inet = IA + IB
IB =
, IA = 
= 8.1μInet = 8.1μ +
Inet = 9μ
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