Refraction is the change in direction of light rays due to a change in the medium they pass through. Wolfram|Alpha provides a wide range of formulas for refraction, including Snell's law, and can be used to compute refractive indices or the position of rainbows. Do computations using the thin lens equation or Fresnel's equation.
Compute the effects of refraction on light in lenses, prisms and raindrops.
Compute the refractive index for a wide variety of substances.