Optics Question 510

Question: A point source of light moves in a straight line parallel to a plane table. Consider a small portion of the table directly below the line of movement of the source. The illuminance at this portion varies with its distance r from the source as

Options:

A) $ E\propto \frac{1}{r} $

B) $ E\propto \frac{1}{r^{2}} $

C) $ E\propto \frac{1}{r^{3}} $

D) $ E\propto \frac{1}{r^{4}} $

Show Answer

Answer:

Correct Answer: C

Solution:

$ I=\frac{Lh}{r^{3}} $



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