Total Internal Reflection

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Light rays from a beam source in air are incident on material that you can vary by moving the slider (position is given in meters and angle is given in degrees).  You can move the beam source and change the angle of the light from the source by clicking on the beam and click-dragging the hotspot.  Restart. 

1. Move the beam source to the new medium.  Use the beam "hotspot" to turn the rays around so they go back toward the air.
2. Drag the beam's "hotspot" to change the angle the light rays make with the normal.  If the rays are along the normal line as they go toward the air (incident angle of zero), what angle do the rays make with the normal in the air?
3. As the angle the incident rays make with the normal in the medium increases from zero, what happens to the angle the rays make with the normal in the air?  Compare/contrast your observations for the rays traveling from the medium to air (this case) to the observations you made when the rays traveled from air to the medium.
4. The critical angle is defined as the incident angle for which there is no light leaving the incident medium.  Change the angle of the beam rays until you see this happen.  This is called Total Internal Reflection.  Try to find an angle where the refracted ray lies on the boundary between the two media.  If you can't make this happen exactly, measure the largest incident angle where there is still light leaving the incident medium.   
5. The index of refraction of glass is 1.5, while the index of refraction of diamond is 2.42.    You have just found the critical angle for glass, repeat this process for diamond.  What do you observe about the critical angle for diamond?
6. A diamond's index of refraction is the property of the stone which makes the diamond appear to sparkle in the light.  Based on your observations, provide a justification for why this might occur.   Hint:  Think about what a diamond would look like if it were cut down the middlle.  Trace a ray of light that enters through the top, perpendicular to the flat facet.