A thin glass lens of refractive index μₗ = 1.50 has focal length 30 cm in air. It is immersed in a liquid of refractive index μₘ = 1.333. Find its focal length in the liquid, including sign.
Options

Question

A thin glass lens of refractive index μₗ = 1.50 has focal length 30 cm in air. It is immersed in a liquid of refractive index μₘ = 1.333. 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=120.00 cm. Here ₗ and ₘ are true subscripts.