A few examples of what you can ask Wolfram|Alpha about:
Reflection & Refraction
compute refractions using Snell's law
do a Fresnel's law computation
compute refraction of light in a prism
do computations using the thin lens equation
explore image reflection in a convex mirror
explore image reflection in a concave mirror
calculate the height of a rainbow
compute a diffraction pattern for a single slit
compute a diffraction pattern for a circular aperture
explore the diffraction pattern and maxima for multiple slit diffraction
get information about a laser (or maser)
compare multiple lasers
Refractive Indices
calculate the refractive index of humid air
determine the refractive index of solid and liquid water
look up the refractive index of a material
find a UV cutoff wavelength for a chemical
compute with the Beer-Lambert law
do f-stop arithmetic
compute subject magnification