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The magnification of an object placed it...

The magnification of an object placed it front of a convex lens of focal length `20cm` is `+2`. To obtain a magnification of `-2` , the object will has 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
uisng, `1/v-1/u=1/f` we have `1/(-2x) +1/x =1/20` or
x=10cm
To have a magnification of -2 the image must be real.
u = -y, v - +2y and f = +20
`:. 1/(2y) + 1/y=1/20` or y=30cm `:. y-x=20cm`
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