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An object is kept at a distance of 16 cm from a thin lens and the image formed is real. If the object is kept at a distance of 6 cm from the same lens, the image formed is virtual. If the size of the image formed are equal, the focal length of the lens will be

Answer» Correct Answer - 11 cm
For real image m = `(-f)/(f+16)`
Virtual `m= (f)/(f+6)`
`therefore (-f)/(f+16) = (f)/(f+16) implies f+16 = -f-6`
`2f = -22 implies f = 11 cm`


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