If the magnification of a virtual image formed by an object 10cm from a convex less is 3; then the focal length of the lens is?

A. 10cm
B. 20cm
C. 25cm
D. 15cm

Correct Answer:

Option D – 15cm

Explanation

M = v/u = 3 = v/30. V = 30m

1/u + 1/v = 1/f = 1/10 – 1/30 = 1/f

(3−1)/30 = 1/f

f=(30/2) = 15cm