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
Explanation
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
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