1. Interactive applet: Fun with Snell’s Law.
Same applet as slide 20, try glass into water.

2. Total Internal Reflection; Fiber Optics
Suppose n2<n1. The largest possible value of sin(2) is 1 (when 2 = 90). The largest possible value of sin(1) is
For 1 larger than this, Snell’s Law cannot be satisfied!
This value of  is called the critical angle, C. For any angle of incidence larger than C, all of the light incident at an interface is reflected, and none is transmitted.
Example: n1=1.5 and n2=1 then sin 1=1/1.5 sin 2=0.667 sin 2.
If you set 1=45, then n1 sin 1=n2 sin 2 has no solution. A ray coming in at a 45 angle cannot pass through the interface and be refracted.

3. 1 < C
1 close to C 1 1
1 > C 1

4. n2
n1>n2 
Ray incident normal to surface is not “bent.” Some is reflected, some is transmitted.
Ray incident normal to surface is not “bent.”
Ray incident normal to surface is not “bent.” Some is reflected,

5. n2
n1>n2 
Increasing angle of incidence…

6. n2
n1>n2 
Increasing angle of incidence…more…

7. n2
n1>n2 
Increasing angle of incidence…more…critical angle reached… some of incident energy is reflected, some is “transmitted along the boundary layer.
Increasing angle of incidence…more…critical angle reached…

8. n2
n1>n2 
Light incident at any angle beyond C is totally internally reflected.

10. application: fiber optics