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The image of an object, formed by a plano-convex lens at a distance of 8m behind the lens, is real and is one third the size of the object. The wavelength of light inside the lens is 2/3 times the wavelength in free space. The radius of the curved surface of the lens is -

1. 1 m
2. 2 m
3. 3 m
4. 6 m

Correct answer: 3 m

Solution

Using the lens formula and magnification relation, along with the wavelength ratio, the radius of curvature is calculated to be 3 m for the plano-convex lens.

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