Optical Description
Total internal reflection can be demonstrated using a semi-circular block of glass or plastic. A "ray box" shines a narrow beam of light (a "ray") onto the glass. The semi-circular shape ensures that a ray pointing towards the centre of the flat face will hit the curved surface at a right angle; this will prevent refraction at the air/glass boundary of the curved surface. At the glass/air boundary of the flat surface, what happens will depend on the angle. Where θc is the critical angle measurement which is caused by the sun or a light source (measured normal to the surface):
- If θ < θc, the ray will split. Some of the ray will reflect off the boundary, and some will refract as it passes through.
- If θ > θc, the entire ray reflects from the boundary. None passes through. This is called total internal reflection.
This physical property makes optical fibers useful and prismatic binoculars possible. It is also what gives diamonds their distinctive sparkle, as diamond has an unusually high refractive index.
Read more about this topic: Total Internal Reflection
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