The lens maker’s equation applies to a lens immersed in a liquid if n in the equation is replaced by n1/n2. Here n1 refers to the refractive index of the lens material and n2 is that of the medium surrounding the lens.
(a) A certain lens has focal length of 79.0 cm in air and a refractive index of 1.55. Find its focal length in water.
(b) A certain mirror has focal length of 79.0 cm in air. Find its focal length in water.