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
Verified Correct Answer: D.
Physical Principles & Numerical Solution
M = \(\frac{v}{u}\) = 3 = \(\frac{v}{30}\). V = 30m
\(\frac{1}{u}\) + \(\frac{1}{v}\) = \(\frac{1}{f}\) = \(\frac{1}{10}\) - \(\frac{1}{30}\) = \(\frac{1}{f}\)
\(\frac{3 - 1}{30}\) = \(\frac{1}{f}
f = \(\frac{30}{2}\) = 15cm
Source: Myschool Past Questions Archive (Record #44735)