Question

A point source is kept at a distance of 1000 m has an illumination l. To change the illumination to 16 I the new distance should become

(a) 250 m

(b) 500 m

(c) 750 cm

(d) 800 cm

Answer 1

Correct option (a) 250 m

Explanation:

For a point source, illuminance at a distance r is given by