What is Snell's law? answer n = c/v = sin i/sin r by extension, n1sini = n2sinr, or n2/n1 = sin i/sin r	What is the equation for the critical angle? answer sin critical angle = 1/n
What is the thin lens equation? answer 1/f = 1/u + 1/v Applies to curved mirrors as well.	What is lens power? answer 1/f where f is the focal length in m. Lens power is measured in diopters.
What is the focal length of two lenses in contact? answer 1/F = 1/f1 + 1/f2	What is the equation for the energy of a photon? answer E = hf where h is Planck's constant and f is frequency.