Snell's Law

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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. 

Recall that when a wave travels from one medium to another, its speed changes.  The index of refraction is a way to measure this change in speed.  The index of refraction, n, is defined as the speed of light in air (300,000,000 m/s) divided by the speed of light in that medium.  Indices of refraction are generally greater than 1.  Different materials have different indices of refraction.

Material Index of Refraction
air 1
water 1.33
glass 1.5
diamond 2.42
  1. The yellow line is perpendicular to the surface and is called the normal.  Move the beam until one of its rays hits the surface on the normal (yellow line).  What happens to the light ray as it changes medium from the black region (air) to the new medium?  Describe the changes in its path using the angle the rays make with the normal.
  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 (incident angle of zero), what angle do the rays make with the normal in the new medium?
  3. As the angle the incident rays make with the normal increases from zero, what happens to the angle the rays make with the normal in the new medium?
  4. For five different incident angles, measure the angle the ray from the source makes with the normal (incident angle) and the angle the refracted ray makes with the normal (refracted angle).  You can use the pink protractor to measure angles.  You can drag the protractor around and click-drag to adjust the angle.  Create a table to collect this data.  
  5. Add columns to your table for the sine of the incident angle and the sine of the refracted angle.  Create a graph with the sine of the incident angle on the x-axis and the sine of the refracted angle on the y-axis.  Find the slope of the best-fit line for your graph.   The slope of your line represents the index of refraction of the new medium.  Do your values agree?

Davidson_physics