question_answer

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 

A)            \[E\propto \frac{1}{r}\]   

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

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

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