A concave lens of focal length f forms an image which is 1/3 times the size of the object. Then, the distance of object from the lens is
Options
(a) 2f
(b) f
(c) 2/3f
(d) 3/2f
Correct Answer:
2f
Explanation:
Given, f = -f ⇒ v = (1/3)u
According to the lens formula, 1/f = (1/v) – (1/u) – (1/f)
= [1/(-1/2)u] + (1/u) – (1/f) 1/f
= [(-3+1)/u] – (1/f)
= -2/u ⇒ u = 2f