Refraction of Light
Review these simulations before attempting this investigation:
Explore Learning - Refraction
PHET - Bending Light
The index of refraction of a medium, n, is the ratio of the speed of light in a vacuum, c, to its speed in the substance, v.
n = c/v
What happens when light enters a medium with a higher index of refraction than the medium it is leaving
(it bends toward the normal.)
What happens when light enters a medium with a lower index of refraction than the medium it is leaving
(it bends away from the normal.) This change of direction of light at the boundary of two media is called refraction.
For any light that is traveling from one medium of index of refraction n1, at angle of incidence θ1, to another medium of index of refraction n2, Snell’s law of refraction describes the angle of refraction, θ2, experienced by the light.
n1 sin θ1 = n2 sin θ2
For air, the index of refraction is equal to 1, because the speed of light in air is nearly equal to the speed of light in a vacuum. Whenever air is the medium of incidence of the light, Snell’s law can be simplified.
n2 = sin θ1/ sin θ2
In this lab, you will measure the angle of refraction of light in a glass slab for a number of different angles of incidence. You then will calculate the index of refraction of the glass. Finally, you will compare the index of refraction for each angle of incidence to verify that it is a constant.
Procedure
Open the simulation “Bending Light” at PhET.
Leave the default for entry material at “Air”. Choose “Glass” for the exit material. Record the index of refraction of glass into the data table.
Choose the protractor and set the laser to an angle of incidence, θ1, at 15°. Recall: angles are always measured from the Normal.
Ignore the reflected ray (the ray that remains in air). Using the protractor, measure the angle of refraction, θ2, of the laser and record.
Repeat steps 4 and 5 of this lab for 30°, 45°, 60° and 75°.
Record the average index of refraction.
Repeat the process for water and mystery substances A&B.
Based upon their refractive indicies, what do mystery substances A & B appear to be?
