ABSTRACT

Comparison is made between Fermat's principle for light and the minimization of area by soap films. The variation of height of a film constrained between perspex plates is shown equivalent to the variation of refractive indices of media through which light may pass. The analogy is used to model the refraction of light as it travels through a prism and lenses, and modelling is extended to seismic waves through the earth. The chapter explores refraction in a prism made of a less dense medium set in a more dense medium of higher refractive index by using a triangular perspex insert. The curved path of the rays of light producing a mirage such as in the desert arises from the increasing refractive index as the light moves upwards through the atmosphere starting from ground level. A medium of uniformly changing density and hence refractive index can be modelled by a soap film within a wedge.