JEE PHYSICS MCQ: RAY OPTICS

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A double convex lens is made of glass which has its refractive index 1,45 for violet rays and 1.50 for red rays. If the focal length for violet ray is

20 \mathrm{~cm}

, the focal length for red ray will be

View answer and explanation

Correct option: B

18 \mathrm{~cm}

Option D (

22 \mathrm{~cm}

) is correct because the focal length is inversely proportional to (refractive index - 1), and the refractive index for red rays is lower.

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