Excel Files for Teaching Caustics of Rainbow and Lenses

Abstract

In this paper, Software is presented for teaching through interactive demonstrations about caustics on rainbows and lenses. At first, we explore the caustics on rainbows since they are amenable to analytic calculations. We find 4 kinds of caustics: 2 internal (of first refraction and reflection) and 2 externals (second refraction and exciting from the back of the drop, and 2nd refraction emerging on the front). We examine caustics of lenses constructed by two spherical surfaces. We explore the ray diagrams and wave fronts and give methods for finding the caustics. We also examine the case of thick lens and the caustics due to reflection.