Reflection and Refraction

[ipmed]

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Why is that light will refract going into a thick medium, and then refract back out without changing its angle.
I have attached an image, in case someone wants to see an example of what I am talking about.

 

[kfcman289]

the law of reflection shows that a line drawn (normal) through the "v" on the bottom will create two angles that are equal to eachother. This should show you that alpha on both the left side and right side (if you extended the normal through the first glass) are equal. If both alphas are equal, and the light is going through the same material, then the refraction angle is equal.

 

[butters221]

When light enters a medium with a higher index of refraction than the medium it is leaving (for example light going from air [index of refraction =1] to glass [index of refraction greater than 1]), the light will change direction toward the normal (to the left in your picture) a certain amount, depending on the difference in index of refraction (greater index of refraction = more toward the normal). Then when it reaches the end of the medium and re-enters the original medium that had a lower index of refraction it will change direction away from the normal by the same angle that it originally changed. The light that comes out is at the same angle.

You can calculate all of this by Snell's law.