Question

If light travels in a medium of Refractive Index 1.4 through a distance 250 m in a given time interval, then how much distance will it cover in refractive index 1.75?

(a) 250 m

(b) 500 m

(c) 200 m

(d) 312.5 m

The question was asked in semester exam.

This key question is from Dispersion, Fermat’s Principle & its Application in section Optics of Engineering Physics II

Answer 1

The correct choice is (c) 200 m

Easy explanation: 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 1st & 2nd  respectively and Geometric distance of 2nd & 1st)

=>            n*1.75=1.4*250

=>            n=200.