PhysicsLAB Lab
Video: Law of Reflection

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The Law of Reflection states that when waves are reflected from an interface, the angle of incidence equals the angle of reflection. The purpose of this lab is to experimentally verify this outcome.
While you view the video clip, there are two methods available for the data collection phase of the experiment. One method would be to place a piece of transparent acetate over your monitor's screen and trace with an overhead projector marker three lines: one incident wavefront, mirror (interface) and one reflected wavefront. A second method would be to make the same three markings but on a printed image captured from the video provided by your teacher. With either method you should NOT move your picture or acetate between markings. Each student is to complete their own, individual experiment.
To complete the diagram on paper, you will need to have one #2 standard pencil, three (3) colored pencils, a ruler, and a protractor. Initially complete all of your analysis in #2 pencil, then trace over it with the appropriate colored pencil. Remember that each ray is perpendicular to each wavefront, and that each normal is perpendicular to its respective interface. The normals must be dotted and the wavefronts should remain equally spaced.
Once you have measured your angles, you need to calculate your experimental error. Since we do not know which angle is "correct" we will calculate our error as a percent difference in which we assume that the "correct" answer is most likely somewhere in-between your two measured values.
Diagram Type
angle of incidence 

angle of reflection 

percent difference 

Each student must have your teacher initial and date their lab page. After you submit your angle of incidence, angle of reflection and percent difference you are to place your lab report in the one-way box.
Completed Diagram Check List
labeled and shaded in color #1: incident wavefront, incident ray with arrow, θi
labeled and shaded in color #2: reflected wavefront, reflected ray with arrow, θr
labeled and shaded in color #3: interface, both normals
written in standard #2 pencil: title and percent difference

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Catharine H. Colwell
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