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The focal length of a thin biconvex lens...

The focal length of a thin biconvex lens is `20 cm`. When an object is moved from a distance of `25 cm` in front of it to `50 cm`, the magni-fication of its image changes from `m_(25) to m_(50)`. The ratio `(m_(25))/(m_(50))` is.

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The correct Answer is:
6
`m = (f)/(f + u) implies m_(25) = (20)/(20 - 25) = -4 "and" m_(50) = (20)/(20 - 50) = -(2)/(3) implies (m_(25))/(m_(50)) = (4 xx 3)/(2) = 6`
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