Question

If a monochromatic light goes through 2 cm of glass or 2.25 cm of water, the optical path is the same. If refractive index of glass is 1.50, then what is the refractive index of water?

(a) 1.33

(b) 1.23

(c) 1.50

(d) 1.13

The question was posed to me during an online interview.

My doubt stems from Dispersion, Fermat’s Principle & its Application in portion Optics of Engineering Physics II

Answer 1

The correct choice is (a) 1.33

For explanation I would say: The product of refractive index of the medium & geometric distance travelled by the light in the medium is known as Optical Path.

=> nA=mB (m&n are refractive index of water & glass  respectively and A&B are geometric distance of glass & water)

=>  2*1.50=m*2.25

=>  m=1.33.