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- 1. Index of Refraction<br />What factors affect the speed of light?<br />
- 2. Light Review<br />Light travels through air at approximately 3.0 x 108m/s.<br />The relationship between speed of light, wavelength, and frequency is expressed in the following equation:<br />λ = wavelength (m) c = speed of light (m/s) <br />ν= frequency (s-1) or (Hz)<br />λ = c<br />ν<br />
- 3. Light Review<br />Let’s look at the equation another way:<br />The relationship between frequency (ν) and wavelength (λ) is constant. If frequency increases the wavelength decreases.<br />One way to change the speed of light is to change the medium or “thing” it is traveling through.<br />c = λν<br />
- 4. For example…<br />Pretend like you are skating on a pond. <br />You skate to the edge, into a snowbank, and what happens?<br />
- 5. You slow down!<br />You travel faster on the pond because it is icy and there is less friction.<br />You travel slower and stop in the snow because it has more friction.<br />
- 6. Speed of light<br />Light waves travel quickly through a vacuum and through gases. Gas has a very low density so light travels through it quickly.<br />
- 7. Speed of Light<br />Liquids are much more dense than gases. Light slows down when it enters a liquid from a gas. This causes the light to bend or “refract.”<br />
- 8. Speed of Light<br />Solids are even more dense than liquids. When light enters a solid it slows down even more. <br />We can determine the identity of a solid by how fast light is traveling through it!<br />
- 9. Terms to Know<br />The angle at which a beam of light changes mediums (gas to liquid, liquid to solid, solid to gas, etc.) is called the angle of incidence (θ1).<br />Air<br />θ1<br />Water<br />
- 10. Terms to Know<br />The angle at which a beam of light bends in the new medium is called the angle of refraction (θ2).<br />Air<br />θ1<br />Water<br />θ2<br />
- 11. Snell’s Law<br />Snell’s Law describes the relationship between the angle of incidence and the angle of refraction. This ratio is called the index of refraction (n). <br />(n1) (sin θ1) = (n2) (sin θ2) <br />Air<br />θ1<br />Water<br />θ2<br />
- 12. Let’s try an example:<br />It is common for scientists to measure the amount of sugar or sucrose in a beverage using the index of refraction. A certain clear lemon-lime drink is analyzed to find the index of refraction. The angle of incidence is __30°__ and the angle of refraction is ___21°___. What is the index of refraction for the liquid?<br />Air (n = 1.000)<br />θ1<br />Lemon-Lime Drink (n=?)<br />θ2<br />
- 13. Example<br />AirLemon Lime Drink<br /> (n1) (sin θ1) = (n2) (sin θ2)<br /> (1.000) (sin 30°) = (n2) (sin 21° ) <br /> (1.000) (sin 30°)= (n2)<br /> (sin 21° )<br /> 1.375 = (n2)<br />
- 14. In the Lab<br />You will measure the index of refraction of three liquid compounds:<br />Water (H2O)<br />Methanol (CH3OH)<br />Glycerol (C3H8O3)<br />
- 15. To measure the angles<br />Use the protractor paper provided. <br />Place the semi circle dish on the top “half” of the protractor. <br />Line up the laser with the angle of incidence. <br />Record the angle of refraction.<br />
- 16. Closure Questions<br />How does the index of refraction of corn oil compare to air? <br />How does the index of refraction of corn oil compare to water?<br />
- 17. Closure Questions<br />How does the index of refraction of corn oil compare to Pyrex® (n=1.474)?<br />
- 18. Closure Questions<br />What factors might change the index of refraction of a solution of 95% methanol in water?<br />
- 19. Closure Questions<br />What are some ways scientists might use the index of refraction to identify materials?<br />
- 20. Index of Refraction Simulator<br />http://phet.colorado.edu/en/simulation/bending-light<br />

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