Session 1, Page 4: Refraction of Light


All forms of electromagnetic radiation travel at the same constant velocity through a vacuum. The term "speed of light" refers to this constant, which is about 186,000 miles per second (~300,000 kilometers per second). However, when light travels through a medium of some density, its velocity is slowed by an amount that corresponds to the density of the medium. When light passes from a transparent medium of one density (such as air) to a transparent medium of a different density (such as glass), its speed is altered causing the light rays bend slightly. This bending of light is called refraction. The degree of refraction depends both upon the density of the refracting medium and the wavelength of the light that is being refracted.

As we can see from Figure 5, the line between one medium and another is called the boundary. The incoming light ray is called the incident ray. The "normal" is an imaginary line at the point of entry of the incident ray, perpendicular to the boundary. After passing the boundary, the light ray is called the refracted ray.	$refraction.gif (3976 bytes)$ Figure 5 When light passes the boundary of two mediums of different densities, the light is refracted due to the change in its velocity.

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