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# A point source emitting light uniformly in all directions

Question:

A point source emitting light uniformly in all directions is placed $60 \mathrm{~cm}$ above a table-top. The illuminance at a point on the table-top, directly below the source, is $15 l u x$. Find the illuminance at a point on the tabletop $80 \mathrm{~cm}$ away from the first point.

Solution: