Students will be able to observe that refraction (bending) always takes place at the interface between two different transparent materials and that the angle of refraction in plastic is smaller than the angle of incidence in air. The light is directed at the center of the semicircular cup where it is bent along a radius and exits the element without bending a second time. Careful measurement of the incident angle and the refracted angle will produce data which may be used to compute a constant ratio of the sine of the angles.