Refraction of Light


Yuri Endo 2012

When a light wave passes from one medium (material) into another with a different density, more precisely, only when there is a difference in the index of refraction between the two media, the wave changes its direction. This change of direction as the wave enters to the second medium is called refraction. In this case, the light changes its direction as it passes from air into glass then back to the air. 


Yuri Endo 2012

>img. 1: A spoon in an empty glass
>img. 2: img. 1 filled with water 

When the glass is filled with water, the spoon appears to be bent through the side of the glass. 

When light passes from a medium of higher density to lower, it bends off the normal (the perpendicular to the surface it strikes) and when it passes from medium of lower density into higher it bends to the normal. In this case, as the light passes from the glass to water, the light slows down and changes its direction and as the light leaves the glass, it picks up its speed again. As a result,  the spoon look as though it is bent since light travels slower through water than through air. 

Yuri Endo 2012

>img. 1: An empty bowl with a coin
>img. 2: img. 1 filled with water
>img. 3: img. 1 filled with corn oil

When the bowl is empty the edge of the bowl prevent us from seeing the coin inside fully. Whereas, when the bowl is filled with water, the light bends over the edge of the bowl and the part of the coin becomes more visible.

The coin appears to be more visible in the oil as compared the water because oil has a higher index of refraction than water or air. In other words, a medium that has higher index of refraction bends light more than another (ex. diamonds).   

This effects of refraction are also responsible for the mirages observed on a hot, sandy desert and the bottom of a pool looking closer to the surface than they actually are.

Reference: Snell's Law , Snell's Law video, Refraction of LightPhysics Aplet: Refraction of Light 

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