A thin glass lens of refractive index μₗ = 1.55 has focal length 40 cm in air. It is immersed in a liquid of refractive index μₘ = 1.400. Find its focal length in the liquid, including sign.
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A thin glass lens of refractive index μₗ = 1.55 has focal length 40 cm in air. It is immersed in a liquid of refractive index μₘ = 1.400. Find its focal length in the liquid, including sign.

G1 Physics · Accepted Answer

For unchanged curvatures, fₘ/fair=(μₗ−1)/(μₗ/μₘ−1), hence fₘ=205.33 cm. Here ₗ and ₘ are true subscripts.