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An object placed 2.4 m in front of a lens produces a clear image on a film located 12 cm behind the lens. A 1 cm thick glass slab of refractive index 1.50 is then inserted between the lens and the film, with its plane surfaces parallel to the film. To obtain a sharp image again on the film, to what distance from the lens must the object be moved?

1. 7.2 m
2. 2.4 m
3. 3.2 m
4. 5.6 m

Correct answer: 5.6 m

Solution

The insertion of the glass slab increases the optical path length due to its refractive index, requiring the object to be moved closer to the lens to maintain a sharp image on the film. The new object distance is calculated based on the effective change in distance caused by the slab, resulting in the correct answer of 5.6 m.

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