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प्रश्न
The focal length of a double convex lens is equal to the radius of curvature of either surface. What is the refractive index of its material?
उत्तर
`1/"f" = ("n"-1) (1/"r"_1 + 1/"r"_2)`
`1/"f" = ("n"-1) (1/"f" + 1/"f")`
`("n"-1) = 1/2`
∴ n = 1.5
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