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Laser Teaching Center, Physics and Astronomy Total Internal Reflection is a phenomenon that can occur when a ray of light passes from one medium to another with a lower index of refraction. If the angle of incidenc at the boundary is larger than the "critical angle" then the ray will be perfectly reflected with no loss of energy. The critical angle can be determined using Snell's Law. The critical angle is equivalent to the angle of incidence at which the angle of refraction is 90 degrees. D.C. Look Jr.[1] used Total Internal Reflection to measure the index of refraction of liquids. The goal of my project is to duplicate his experiment in order to understand the uncertainties of the method. In Look's experiment, a laser beam was directed normal to the surface of a liquid, creating a diffused reflection by placing a white sheet of paper directly under the water. While some of the light rays escaped the liquid, some undergo total internal reflection. This is why you observe a dark circle with light around it. By measuring the radius of the circle and the depth of the water, one is able to measure the index of refraction of the liquid used in the experiment. I am working on duplicating this experiment in order to measure the index of refraction of water.
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