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The plane faces of two identical planoco...

The plane faces of two identical planoconvex lenses each having focal length of `40 cm` are pressed against each other to form a usual convex lens. The distance from this lens, at which an object must be placed to obtain a real, inverted image with magnification one is

A

80 cm

B

40 cm

C

20 cm

D

162 cm

Text Solution

Verified by Experts

The correct Answer is:
B

`(1)/(f_(eq)) = (1)/(f_(1)) + (1)/(f_(2)) `
`rArr (1)/(f_(eq)) = (1)/(40) + (1)/(40) rArr " " f_(eq) = 20 ` cm
At centre of curvature m = 1
`therefore " " u = R = 2f_(eq) = 40 ` cm.
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