An object placed on the principle axis of a convex lens of focal length 10m produces a real image of double magnification. The image distance from the lens is
-
A.
30cm -
B.
25cm -
C.
20cm -
D.
15cm -
E.
10cm
Correct Answer: Option A
Explanation
(frac{1}{v}) + (frac{1}{u}) = (frac{1}{f})
(frac{1}{v}) = +ve real image distance
where; U = +ve real object distance
f = real focus = 10
m = magnification
M = 2 = (frac{v}{u})
2u = V
(frac{1}{2u}) + (frac{1}{u}) = (frac{1}{10})
2u = 30
u = 15cm
v = 2u = 2 x 15
= 30cm