STRAIGHT OR BENT...THAT IS THE QUESTION

It has been shown that light travels in rays. Light also wants to get to a certian destination in the shortest possible time. Therefore, in order to accomplish that, regardless of how fast the ray might be traveling, the light ray will bend to reach its destination in the shortest amount of time. This theory is known as Fermat's Principle.

Now depending on the type of material the light ray is entering and leaving, determines how much the light slows down and the new path of travel. When traveling from a high index of refraction to a low index of refraction the light increases in velocity and bends away from the normal. And when traveling from a low index of refraction to a high index of refraction, the light decreases in velocity and bends towards the normal.

Each material has its own index of refraction. Some common indicies of refraction include:

	AIR                1.0003 
	WATER              1.33
	ETHYL ALCOHOL      1.36
	GLASS
	  -- QUARTZ        1.46
	  -- CROWN   	   1.52
	  -- FLINT         1.58
	SODIUM CHLORIDE    1.53
        LUCITE  	   1.57
        DIAMOND  	   2.42

The angle at which the light is entering the second medium is called the Angle of Incidence. The angle the light creates with the normal after entering the second medium is called the Angle of Refraction.

The light ray travels from a low index of refraction to a high index of refraction causing the ray to bend towards the normal.

The diagram would be flipped 180 degrees if the light was traveling from a higher index of refraction to a lower index of refraction.

To determine the speed of light in each medium, you would divide the speed of light in a vacuum by the index of refraction.

                         v = c/n
For example: if light is traveling through water, the speed would be
                         v = (3x10^8 m/s)/1.33
            
                         v = 2.23x10^8 m/s

You can use this equation to obtain the speed of light in various other materials as well.