PhysicsLAB AP Free Response Question
2013 B3

A student is asked to experimentally determine the index of refraction of the semicircular block of transparent plastic shown in the figure below.
The student aims a red laser beam of wavelength = 632 nm at the center of the flat side of the block, as shown. The ray is refracted from air into the plastic and strikes the semicircular side of the block perpendicularly. The student uses a protractor to aim the laser at several different angles of incidence between 0º and 90º and to measure the angles of refraction . The student’s data are given in the table below.
(a) On the grid below, plot data that will allow the index of refraction of the plastic to be calculated from a straight line that represents the data. Clearly label the axes, including the scales.

 (b) On your graph, draw a straight line that best represents the data. Use the slope of the line to determine the index of refraction of the plastic.

 (c) The student now wants to confirm the result obtained in part (b) by using the critical angle for the plastic. Describe one experimental method the student can use to measure the critical angle. Indicate how the index of refraction can be determined from this measurement.

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