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

Question

Philoid · Accepted Answer

Let d be the distance between the parallel straight lines and the angle between them is θ.

Intensity is given by,

Using above figure, we get

So, correct option is C.