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Boundaries and Waves Tour

Critical Angle

The Critical angle is defined by the angle at which all power is reflected and none is transmitted. A critical angle only exists for a wave incident on a medium of lower permitivity than that which it is traveling in. The critical angle arises from the fact that at the boundary the waves in both mediums must be in phase. As the incident angle increases the distance between phase fronts gets smaller and smaller. At the critical angle the transmitted wave's phase fronts are as close as they can get (Transmitted angle is 90 degrees). If the incident angle increases slightly more the transmitted wave becomes evanescent and all the power is reflected.