Optical Refraction with a Toy Robot

A mechanical model of light propagation helps to show that optical refraction is related to the speed of light and how it changes from one medium to another. A tricycle toy robot is used to realize the model. Left and right wheels independently change their speed (high or low) in response to the local color (white or black, respectively) of the ground pattern detected by the corresponding optical sensor. Because of this simple rule the robot path deviates when passing, for example, from a clear to a dark area, in this way mimicking the refraction of a beam of light at an air--glass interface. Black silhouettes, representing optical components, are positioned on a clear mat along the robot trip. The robot trajectories reproduce phenomena such as refraction and total internal reflection showing a perfect analogy to light path described by geometrical optics in a sort of live ray-tracing.