If the magnification of a virtual image formed of an object 10cm from a convex lens is 3, then the focal length of the lens is
-
A.
10cm -
B.
15cm -
C.
16cm -
D.
19cm -
E.
20cm
Correct Answer: Option B
Explanation
V = 3u, U = 10cm
therefore U = -ve,
F = (frac{UV}{U + V})
= (frac{10 times (-30)}{10 – 30 })
= 15cm