PhysicsLAB AP Free Response Question
2006 B4

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A student performs an experiment to determine the index of refraction n of a rectangular glass slab in air. She is asked to use a laser beam to measure angles of incidence  in air and corresponding angles of refraction  in glass. The measurements of the angles for five trials are given in the table below.
 (a) Complete the last two columns in the table by calculating the quantities that need to be graphed to provide a linear relationship from which the index of refraction can be determined. Label the top of each column.

(b) On the grid below, plot the quantities calculated in (a) and draw an appropriate graph from which the index of refraction can be determined. Label the axes.

 (c) Using the graph, calculate the index of refraction of the glass slab.

The student is also asked to determine the thickness of a film of oil (n = 1.43) on the surface of water (n = 1.33). Light from a variable wavelength source is incident vertically onto the oil film as shown below.
The student measures a maximum in the intensity of the reflected light when the incident light has a wavelength of 600 nm.
(d) At which of the two interfaces does the light undergo a 180º phase change on reflection?

 (e) Calculate the minimum possible thickness of the oil film.

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