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Reflection and Refraction

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Submitted By minidancegirl
Words 576
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The purpose of this lab was to experimentally apply the concepts of the law of reflection and Snell’s law to reflected and transmitted light using a beam of light, a mirror, a plexiglass prism, and a small container of water.
The law of reflection states that Θi = Θr (the angle of incidence is equal to the angle of reflection). Transmitted light is subject to Snell’s law, which holds that n1sinΘ1 = n2sinΘ2, where n is the medium’s distinct index of refraction.
Using a tabletop setting, a beam of light was first directed towards a mirror at three distinct angles (small, medium, and large). Diagrams were drawn and the angles of incidence and reflection were calculated from measured αi and αr (the angles between the rays of light and the mirror surface). To investigate Snell’s law, a beam of light was directed at a plexiglass prism at three distinct angles (small, medium, and large). Diagrams were constructed and the measured angles α1, α2, α3, and α4 were used to calculate Θ1, Θ2, Θ3, and Θ4. Using these values and the accepted index of refraction for air (n = 1.00), experimental indices for plexiglass were calculated from Snell’s law (n1sinΘ1 = n2sinΘ2). To further investigate Snell’s law using another medium, a beam of light was passed through a container of water. A diagram was drawn and Θ1, Θ2, Θ3, and Θ4 were calculated from measured angles α1, α2, α3, and α4. Using these Θ values and the accepted index of refraction for air, an experimental index of refraction for water was calculated from Snell’s law.

The following angles were measured (α) and calculated (Θ) to investigate the law of reflection:

Angle of Incidence αi Θi αr Θr
Small
85.1°
4.9°
84.0°
6.0°
Medium
77.2°
12.8°
75.1°
14.9°
Large
69.2°
20.8°
69.0°
21.0°

According to the law of reflection, Θi = Θr. Our experimental Θi and Θr did not match up perfectly; however, these values were very close, particularly when a large angle of incidence was used.

Experimental indices of refraction (plexiglass and water) were calculated using Snell’s law from the following measured (α) and calculated (Θ) angles:

Angle of Incidence α1 Θ1 α2 Θ2 α3 Θ3 α4 Θ4
Small (Plexiglass)
85.0°
5.0°
86.0°
4.0°
86.5°
3.5°
85.2°
4.8°
Medium (Plexiglass)
76.0°
14.0°
77.1°
12.9°
79.0°
11.0°
77.0°
13.0°
Large (Plexiglass)
53.3°
36.7°
64.0°
26.0°
63.2°
26.8°
53.4°
36.6°
Water
52.5°
37.5°
60.0°
30.0°
61.0°
29.0°
52.9°
37.1°
The accepted index of refraction for plexiglass is n = 1.49. The large angle of incidence yielded an experimentally-calculated index of refraction closest to the accepted value (nexp. = 1.34, 10.1% error). The index of refraction (plexiglass) calculated from the medium angle of incidence was n = 1.1315 and n = 1.31 from the small angle of incidence.

The accepted index of refraction for water is n = 1.33. Our experimental index of refraction (calculated from Snell’s law) was n = 1.231 (7.4% error).

This experiment confirmed the law of reflection. Although our experimentally-derived indices of refraction did not align perfectly with the accepted values for plexiglass and water, the results were relatively close. Repeating each experiment several times may help to reduce future error.

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