Video Transcript: Law Enforcement: Refraction
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This is the boundary between air and glass. And this is the normal line. And this is a light ray refracting (or bending) at the boundary. We say the light refracts towards the normal line. The incident ray is farther from the normal line than the refracted ray is. When does this happen?
It happens whenever light passes from a less optically dense medium into a more optically dense medium. Since density is inversely proportional to speed (v) and directly proportional to the index of refraction (n), it also happens when light passes from a low-n to a high-n medium and when it changes speed from fast (large v) to slow (small v).
What happens when light passes from a more dense to a less dense medium? The light ray refracts away from the normal line. The refracted ray is farther from the normal line than the incident ray is. This occurs for light passing from a optically more dense to a less optically dense medium, from a high-n to a low-n medium, and changes speed from slow (small v) to fast (large v).
So by observing how light refracts – towards or away from the normal – you can make predictions regarding the relative optical density, light speed within, or index of refraction of the two media. The rules work whether the boundary is horizontal or vertical or oriented in any such direction.
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