P. 4454. The volume of a cubic aquarium, which is filled with water halfway, is V=8 litres. Salt is carefully dissolved in the water such that the refractive index of the water, with respect to light which illuminates the water from below, changes with the height h measured from the bottom of the aquarium as a function of n(h)=n0-kh2, where n0=1.35 is the refractive index at the bottom and k=2 m-2 is a constant.
The aquarium is illuminated by a light-beam perpendicularly to one of its side. On the other side a screen is moved. The screen always remains parallel to that side of the aquarium which is illuminated by the light. How far is the screen from the aquarium, when only a thin sharp, horizontal line of light can be observed on it?
Deadline expired on 11 June 2012.