FYKOS Year 28 Series 5 Problem 5 — a lens was floating on water · FYKOS 28 #28.5.5

Physics · mechanics · optics

Problem

On the surface of water a thin biconcave lens made from a light-weight material is floating. The radii of both surfaces are

R=20\;\mathrm{cm}

. Determine the distance between the two focal points of the lens, if the index of refraction of the air above the lens is

n_{a}=1

, index of refraction of the lens is

n_{l}=1.5

and index of refraction of water is

n_{w}=1.3

. Bonus: Assume that it is a lens of width

T=3\;\mathrm{cm}

, and within it is symmetrically place an air bubble in the shape of a biconcave lens with the radii of curvature

r=50\;\mathrm{cm}

and width

t=1\;\mathrm{cm}