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A convex lens is place over a plane mirr...

A convex lens is place over a plane mirror. A pin is now positioned so that there is no parallax between the pin and its image formed by this lens-mirror combination . How can this observation be used to find the focal length of the convex lens? Give appropriate reasons in support of your answer.

Text Solution

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The rays must fall normally on the plan mirror so that the image of the pin coincide with itself.

Hence rays, like CA and DB form a parallel beam incident on the lens.
`:.` P is the position of the focus of the lens.
`:.` Distance OP equals the focus length of the lens.
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