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The Direction of Bending:
Refraction is the bending of the path of light as it passes across the boundary between two media. The direction of refraction is dependent upon the relative speed at which light moves within the two media. The rules are:
- When light passes from a medium in which it travels faster into a medium in which it travels slower, the light ray will refract towards the normal line.
- When light passes from a medium in which it travels slower into a medium in which it travels faster, the light ray will refract away from the normal line.
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Optical Density, Speed of Light and Index of Refraction:
The speed at which light travels through a medium is dependent upon the optical density of that medium. Light travels fastest in media that are least optically dense. The index of refraction value provides a relative measure of the optical density of a material. The higher the index of refraction value, the more optically dense a material is and the slower that light will travel in that material.
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Carefully inspect the diagram and observe the direction that light refracts at the boundary - either towards or away from the normal. From the direction of bending, identify which medium is the one in which light travels slowest. This is the medium that is most optically dense and has the greatest index of refraction value. Take your time and use your noodle (that's your brain).
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