The magnification of an object placed in front of a convex lens is `+2` . The focal length of the lens is `2.0` metres. Find the distance by which object has to be moved to obtain a magnification of `-2` (in metres).

Answer

2

Explanation

For magnification `+2, u=-x, v=-2x ` and `f=2.0m`
From `(1)/(v)-(1)/(u)=(1)/(f)`, we have `(1)/(-2x)+(1)/(x)=(1)/(z)`
`x=1.0m`
For magnification of `-2, u=-y, V=+2y, f=2.0m`
we have `(1)/(2y)+(1)/(y)=(1)/(2)rArr y=3.0m`
So distance to be moved `=y-x=3-1=2m`