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Snell's Law. By: Brown Sugar, Oatmeal, and Skim Milk* aka Ali Rangwala, Apoorva Sharma, and Zachary Praiss. *All parts of a healthy breakfast. Purpose. Investigate the relationship between the angle of incidence and the angle of refraction for an air-plastic and an air-water interface.
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Snell's Law By: Brown Sugar, Oatmeal, and Skim Milk* aka Ali Rangwala, Apoorva Sharma, and Zachary Praiss *All parts of a healthy breakfast.
Purpose Investigate the relationship between theangle of incidence and the angle of refraction for an air-plastic and an air-water interface.
Angles Normal Line Angle of Incidence θi θr Angle of Refraction
Semi-Chords Normal Line Incident Semi-Chord Di Dr Refracted Semi-Chord
Hypothesis We predicted that the angle of refraction would be directly proportional to the angle of incidence.
Equipment - Laser - Semicircular water container - Plaster semicircle - Reference circle - Protractor - Ruler
Setup Angle of Incidence Angle of Refraction
Air-Plastic Apparatus Laser Plastic
Air-Water Apparatus Laser Water
Procedure • Set up apparatus as shown. • Shine laser beam at an angle of 0° from the normal line. • Record position of refracted beam on circle. • Repeat for 10°, 20°, 30°, 40°, 50°, 60°, 70°, and 80°. • Measure angles of refraction and semi-chords of incidence and refraction.
Raw Data Air → Plastic Air → Water
Mathematical Analysis: Air→Plastic Semi-Chord of Incidence → Di Semi-Chord of Refraction → Dr Dr ∝ Di Dr = kDi k = ΔDr/ΔDi k = 0.652 (From Logger Pro) Dr = 0.652 Di
Mathematical Analysis: Air→Water Semi-Chord of Incidence → Di Semi-Chord of Refraction → Dr Dr ∝ Di Dr = kDi k = ΔDr/ΔDi k = 0.7414 (From Logger Pro) Dr = 0.7414 Di
Mathematical Analysis: Air→Plastic Angle of Incidence → θi Angle of Refraction → θr sin(θr) ∝ sin(θi) sin(θr) = k sin(θi) k = Δsin(θr)/Δsin(θi) k = 0.6655 (From Logger Pro) sin(θr) = 0.6655 sin(θi)
Mathematical Analysis: Air→Water Angle of Incidence → θi Angle of Refraction → θr sin(θr) ∝ sin(θi) sin(θr) = k sin(θi) k = Δsin(θr)/Δsin(θi) k = 0.7504 (From Logger Pro) sin(θr) = 0.7504 sin(θi)
Error Analysis for Semi-Chord's index of Refraction Semi-Chords Plexiglass Absolute Error = |ACC - EXP| Absolute Error = |1.51 – 1.53| Absolute Error = 0.02 Relative Error = (Absolute Error) / ACC Relative Error = (0.02) / 1.51 Relative Error = 1.32% Semi-Chords Water Absolute Error = |ACC - EXP| Absolute Error = |1.33 – 1.35| Absolute Error = 0.02 Relative Error = (Absolute Error) / ACC Relative Error = (0.02) / 1.33 Relative Error = 1.50%
Error Analysis for Sin(θ)'s Index of Refraction Plexiglass Absolute Error = |ACC - EXP| Absolute Error = |1.51 – 1.50| Absolute Error = 0.01 Relative Error = (Absolute Error) / ACC Relative Error = (0.01) / 1.51 Relative Error = 0.662% Water Absolute Error = |ACC - EXP| Absolute Error = |1.33 – 1.33| Absolute Error = 0 Relative Error = (Absolute Error) / ACC Relative Error = (0) / 1.33 Relative Error = 0%
Sources of Error Inaccuracies while tracing the laser and measuring the angles. Impurities in the water and the plexiglass varying from typical plexiglass causing the light to travel at a different speed through those materials. Plastic container of water slightly refracted the water for the trials involving the angle of refraction for water.
Conclusion k = n1/n2 where n is specific indices of refraction for specific materials sin(θr) = k sin(θi) sin(θr) = n1/n2 sin(θi) n1sin(θ1) = n2sin(θ2) → General Model where n is the index of refraction or the ratio of the speed with which light travels through a vacuum over the speed light travels through a given medium.
Ray Diagram Normal Line Angle of Incidence θi θr Angle of Refraction