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The magnification of an object plac ed i...

The magnification of an object plac ed in front of a convex lens of focal length 20 cm is +2. to obtain a magnification of -2. the object will have to be moved a distance equal to

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When magnification is +2 then the image is virtual. Both the image and the object are on the same side of the lens `u=-x,v =-2x, f=+20`
Using `1/v-1/u=1/f` we have `1/(-2x)+1/x=1/20 or x=10 cm`
To have a magnification of -2 the image must be real.
`u=-y, v=+2y and f=+20`
`therefore 1/(2y)+1/y=1/20 or y=30 cm therefore y-x=20 cm`
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