A beam of light is refracted at the border between to media.

The index of refraction of each media and the inbound angle of the beam of light can be changed.

Instructions
 

n1 = Index of refraction of the "inbound" material

n2 = Index of refraction of the "outbound" material

alpha = Angle between inbound ray of light and perpendicular

beta = Angle between outbound ray of light and perpendicular

To change alpha either use your mouse to drag the inbound ray of light or type the desired angle into the box and confirm changes with the Return key.
To change the index of refraction, type the desired value into the appropriate box.