The laminated card included with the Refraction Bottle (a red-capped culture flask) asks "Does light always travel in a straight line?"

Light does travel in a straight line through air or another homogeneous medium. However, when it must pass through an interface of between two different materials (air and water for instance), its path is redirected, in a process called refraction.

For the Refraction Bottle, light rays are bent at the interface between the outside air and the water-filled plastic bottle. Lines are drawn on the laminated sheet underneath, simulating uninterrupted straight-line paths of light rays in air. When the bottle is placed in the path of the light ray, the ray is bent from its original path. This is made visible as the lines drawn below the bottle are clearly no longer continuous, and bend noticeably at the bottle interface.

Place the water-filled bottle at an angle over the colored lines, as suggested by the dotted lines. Look into the bottle from the front, not the top, looking into the plane face of the square bottle. You should see the straight line enter the bottle, and then exit behind the bottle, seemingly shifted a centimeter or so to the right. This redirection is the result of two instances of refraction; one ray-bending as the light enters the bottle, and another as it exits.

Copyright 2004 Straley/Pinney - The University of Kentucky Physics Petting Zoo