When the angle of incidence is increased beyond the critical angle, refraction can no longer occur, because the angle of refraction cannot increase to more than 90o. Instead, total internal reflection occurs, where all the light is reflected back into the object, according to the laws of reflection.
| Definition: Total Internal Reflection |
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| Total internal reflection is the complete reflection of a light ray in an optically denser medium at the boundary with an optically less dense medium. |
| Two conditions required for total internal reflection to occur: |
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| 1. The light ray must travel from a material with higher refractive index towards a material with lower refractive index.
2. The angle of incidence of the light ray must be greater than or equal to the critical angle of the medium. |
| Example 7 |
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The diagram below (not drawn to scale), shows a right-angled glass prism ABC of refractive index 1.5. Angle at A is 30°. Two rays of light are incident normally on the face AB and face BC of the prism at points P and Q respectively. Draw the path of these rays (in the two separate diagrams) until it emerges out of the prism. Mark all relevant angles and show clearly all necessary calculations.
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| Links |
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| Some interesting pictures taken under a swimming pool are shown on the following page: http://wordpress.mrreid.org/tag/refraction/ |