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The magnification of an object placed in...

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).

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The correct Answer is:
2
For magnification ` (m) = + 2, u = - x, v = - 2 x and f = 2 m`
From ` (1)/( v) - (1)/(u) = (1)/(f) ` , we have `(1)/(-2x) + (1)/(x) = (1)/(2)`
` x = 1.0 m`
For magnification `(m) = - 2, u = - y, v = + 2y, f = 2.0 m`
We have `(1)/(2y) + (1)/(y) = (1)/(2) rArr y = 3.0 m`
So, distance to be moved ` = y - x = 3 - 1 = 2 m`
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