Classical Mechanics (Kibble & Berkshire) · Problem 13.8
Hamilton's equations and phase space — T.W.B. Kibble, F.H. Berkshire
Physics — Mechanics · fermats-principle
Problem
A sugar solution has a refractive index n that increases with the depth z according to the formula
n=n0(1+az)1/2,
where n0 and a are positive constants. A particular ray is horizontal when it passes through the origin of coordinates. Show that the path of the ray is not the straight line z=0 but the parabola z=x2/4a.