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A plano - convex lens having radius of curvature of first surface 2 cm exhibits focal length of f 1 in air. Another plano - convex lens with first surface radius of curvature 3 cm has focal length of f 2 when it is immersed in a liquid of refractive index 1.2. If both the lenses are made of same glass of refractive index 1.5, the ratio of f 1 and f 2 will be : -

1. 3 : 5
2. 1 : 3
3. 1 : 2
4. 2 : 3

Correct answer: 1 : 3

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