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1. The speed of light in a glass
References:
1.http://en.wikipedia.org/wiki/Refraction
2.Essential University Physics/Richard Wolfson---Volume 2
3.http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr2.html#c1
4.http://howthingsworkclass.blogspot.fi/2012/10/reflection-and-refration-reflection.html