Give the limiting refractive index of a rainbow.
The raindrops are modelled as spherical droplets, with refractive index $n$, with parallel rays from the Sun incident on it. I have a very limited knowledge on this area, so know nothing about Fresnel Coefficients or Snell's Law etc., so I would appreciate an answer which starts simple then gradually builds up if necessary. I'm looking simply for the physics which should enable me to tackle this problem so don't be under the impression that I'm just looking for the answer.