A point source of light is placed at a distance, of 2 f from a converging lens of focal length 1 The intensity on the other side of the lens is maximum at a distance
(a) f
(b) between f and 2 f
(c) 2 f
(d) more than 2 f.
The correct answer is (c) 2 f
EXPLANATION:
The intensity of the light on the other side is maximum where the image of the point source is formed.
Here u = -2f, f = f, hence from the lens formula 1/v -1/(-2f) = 1/f
→1/v = 1/f -1/2f = 1/2f →v = 2f
Hence the image will be formed at 2f distance from the lens on the other side.