Refraction
As light travels by wave, it can be refracted, reflected, or absorbed. In a vacuum where there are no interfering particles, light travels at a constant speed. When light interacts with an object or material, its speed is slowed (Jacobs, G. & Schulman, J., 2005). In addition to changing its speed, the wavelength and direction can be altered based on its interaction with a material (Jacobs, G. & Schulman, J., 2005). When passing through the surface of one transparent material and another, the light rays bend in the act of refraction; the change in the wavelength results in a change of direction for the actual light beam yet the frequency of the wavelength remains unchanged (Koch, 2013). See Figure 2 below for a visual example of refraction: