Refraction and Total Internal Reflection Total internal reflection is just the result of refraction at a large angle. Have a look at the diagrams below. When light passes from a denser medium (water) into a less dense medium (air), the light is bent away from the normal line (a line perpendicular to where the light crosses the boundary). This is called refraction. It's why a spoon in a glass of water appears bent. Light always bends when it passes from one medium to another, if their refractive indicies are different.   If the light hits the boundary at a large enough angle from the normal line, it will bend (refract) right back into the water! The light refracting downwards makes it look as if the light reflected off the boundary. This is called total internal reflection. Light does this when the angle at which it hits the boundary reaches the critical angle for that material. The refractive index of a material can be calculated using the formula: where n  is the refractive index of the material, c  is the speed of light in a vacuum, and v  is the speed of light in the material. Since the speed of light in a vacuum (c) is the fastest that light can travel, v  will always be less than c. So the refractive index n  of a material will always be a number greater than 1.

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