Refraction is the bending of light as it passes from one medium to another. The light changes speed and direction. The wavelength of the light will change but not its frequency. Refraction occurs when light passes between water and air, and is responsible for causing objects to appear larger than they are, as well as Snell’s Window. Here is a visual demonstration: http://www.ps.missouri.edu/rickspage/refract/refraction.html