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
Verified Correct Answer: D.
Physical Principles & Numerical Solution
M = \(\frac{v}{u}\)
v = mu = 4 x 25 = 100m
\(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\)
\(\frac{1}{100} + \frac{1}{25} = \frac{1}{f}\)
f = 20cm
Source: Myschool Past Questions Archive (Record #34219)