Question

The magnification of an object placed in front of a convex lens is +2. The focal length of the lens is 2 metres. Find the distance by which object has to be moved to obtain a magnification of -2 (in metres). ___

Answer 1

For magnification +2, u=-x, v=-2x and f = 2m
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$ we have, $-\frac{1}{2x}+\frac{1}{x}=\frac{1}{2}$
$x=1m$
for magnificaion of -2, u=-y, v = +2y, f = 2m
$\frac{1}{2y}+\frac{1}{y}=\frac{1}{2}$
y = 3m
(y - x)= 2m