Refraction: Refraction occurs when a wave travels from one medium to another.  The light rays are said to be “bent”.  You can see this in a glass of water.  Place a pencil in the glass – the pencil looks like it is broken, shifted to the side, and larger in the water.

This occurs because light rays from the pencil are bent as they travel through the water.

 Refraction of light  º  change in the path direction in a different medium.

This brings us to a very important concept.  The index of refraction. 

Snell’s Law:  The amount of refraction is of great interest to we physicists – you are interested are you not? 

If the light rays travel from one medium into another, they will be bent. 

In the drawing to the right, the angle of incidence is q_I, the angle of refraction is q₂.  These angles are measured relative to a normal to the surface of the boundary between the two substances.

The amount of refraction, that is, the angle of refraction, is related to the angle of incidence by Snell’s law.  The drawing to the right shows a ray of light passing from one medium into another.  In the first medium it has an index of refraction of n₁  in the second medium its index of refraction is n₂.  Here is Snell’s law:

n₁ is the index of refraction in the first medium, n₂ is the index of refraction in the second medium, q₁ is the angle of incidence, and q₂ is the angle of refraction.

You will be provided with Snell’s law in your data booklet. 

For all practical purposes, the index of refraction in air is 1.                                                                                                        Therefore:      

Let’s look at a typical problem.

·        A Beam of light is traveling in air and is incident on slab of transparent material.  The angle of incidence is 32.0°.  The refracted beam makes an angle of 20.5°.  (a) Find the index of refraction for the slab.

(a)