If a substance is behaving as convex lens in air and concave lens in water then which one of the following is its refractive index?

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Q: 87 (NDA-II/2008)
If a substance is behaving as convex lens in air and concave lens in water then which one of the following is its refractive index?

question_subject: 

Science

question_exam: 

NDA-II

stats: 

0,17,22,7,11,17,4

keywords: 

{'refractive index': [0, 1, 1, 5], 'concave lens': [0, 1, 6, 5], 'convex lens': [0, 0, 0, 4], 'air': [1, 0, 0, 0], 'water': [65, 15, 80, 129], 'substance': [2, 1, 7, 7]}

The given question describes a situation where a substance acts as a convex lens in air and as a concave lens in water.

Option 1 states that the refractive index of the substance is smaller than air. This option is not correct because if the substance is behaving as a convex lens in air, it means that light rays are converging. In this case, the refractive index should be greater than air, not smaller.

Option 2 states that the refractive index of the substance is greater than both air and water. This option is not correct because if the substance acts as a concave lens in water, it means that the light rays are diverging. In this case, the refractive index should be smaller than water, not greater.

Option 4 states that the refractive index is almost equal to water. This option is not correct because if the substance acts as a convex lens in air, the refractive index should be greater than air. It cannot be equal to water.

Option 3 states that the refractive index is greater than air but lesser than water. This option is correct. If the substance behaves as a convex lens in air and a concave lens in water, it means that the refractive index is greater than air but lesser than

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