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A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? Give reason.

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#### Solution

`1/f = (μ - 1) (1/R_1 - 1/R_2)`

`1/f = (μ_m/μ_w - 1) (1/R_1 - 1/R_2)`

`μ_m/μ_w = 1.25/1.33`

`μ_m/μ_w` = 0.98

The value of (µ – 1) is negative and ‘f’ will be negative. So it will behave like diverging lens.

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