1. PW3 - Refraction

2.  When light passes from glass into air (an optically less dense medium), it refracts away from the normal.

3.  When light travels into a less dense medium and the refracted ray is equal to 90 o from the normal:  The refracted ray then runs parallel to the interface (see red arrow in diagram)  The light ray is then “contained” inside of the original medium as it cannot pass through  This special angle of incidence that results in an angle of refraction being 90 o is called the critical angle of that medium.  Substances that have a high index of refraction (n) have a low critical angle.  i.e.: Diamond has an index of refraction of 2.42 with a critical angle of 24.5°  i.e.: water has an index of refraction of 1.33 and a critical angle of 49°.

4.  When light passes into a less optically dense medium with the angle of incidence greater than the critical angle, the light simply reflects off the surface.  It does not pass through and refract.  We call this total internal reflection.  The critical angle can be found using the formula n 1 sinθ 1 = n 2 sinθ 2

5.  What is the critical angle of crown glass (n = 1.52) if light passes from crown glass into air?  (Remember that critical angle is always a unique incident angle.)