A converging lens produces an image four times as large as an object placed 25cm from the lens. Calculate its focal length.

A. 100cm
B. 33cm
C. 29cm
D. 20cm

Correct Answer: Option D

D. 20cm

Explanation

M = v/u

v = mu = 4 x 25 = 100m

1/v+1/u=1/f

1/100+1/25=1/f

f = 20cm