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Question
A converging lens has a focal length of 10 cm in air. It is made of a material with a refractive index of 1.6. If it is immersed in a liquid of refractive index 1.3, find its new focal length.
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Solution
`1/f_a = (1.6 - 1)(1/R_1 - 1/R_2)` ...(1)
`1/f_ℓ = [1.6/1.3 - 1](1/R_1 - 1/R_2)` ...(2)
From equation (1) and (2)
`f_ℓ/f_a = [0.6/0.3 xx 1.3]` ⇒ fℓ = 2.6 × 10 cm ⇒ fℓ = 26 cm
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