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
Verified Correct Answer: A.
Physical Principles & Numerical Solution
\(\frac{1}{v}\) + \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{v}\) = +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
Source: Myschool Past Questions Archive (Record #29026)