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
Explanation
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