Index of refraction
- 1. Index of RefractionWhat factors affect the speed of light?
- 2. Light ReviewLight travels through air at approximately 3.0 x 108m/s.The relationship between speed of light, wavelength, and frequency is expressed in the following equation:λ = wavelength (m) c = speed of light (m/s) ν= frequency (s-1) or (Hz)λ = cν
- 3. Light ReviewLet’s look at the equation another way:The relationship between frequency (ν) and wavelength (λ) is constant. If frequency increases the wavelength decreases.One way to change the speed of light is to change the medium or “thing” it is traveling through.c = λν
- 4. For example…Pretend like you are skating on a pond. You skate to the edge, into a snowbank, and what happens?
- 5. You slow down!You travel faster on the pond because it is icy and there is less friction.You travel slower and stop in the snow because it has more friction.
- 6. Speed of lightLight waves travel quickly through a vacuum and through gases. Gas has a very low density so light travels through it quickly.
- 7. Speed of LightLiquids 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.”
- 8. Speed of LightSolids are even more dense than liquids. When light enters a solid it slows down even more. We can determine the identity of a solid by how fast light is traveling through it!
- 9. Terms to KnowThe 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).Airθ1Water
- 10. Terms to KnowThe angle at which a beam of light bends in the new medium is called the angle of refraction (θ2).Airθ1Waterθ2
- 11. Snell’s LawSnell’s Law describes the relationship between the angle of incidence and the angle of refraction. This ratio is called the index of refraction (n). (n1) (sin θ1) = (n2) (sin θ2) Airθ1Waterθ2
- 12. Let’s try an example: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?Air (n = 1.000)θ1Lemon-Lime Drink (n=?)θ2
- 13. ExampleAirLemon Lime Drink (n1) (sin θ1) = (n2) (sin θ2) (1.000) (sin 30°) = (n2) (sin 21° ) (1.000) (sin 30°)= (n2) (sin 21° ) 1.375 = (n2)
- 14. In the LabYou will measure the index of refraction of three liquid compounds:Water (H2O)Methanol (CH3OH)Glycerol (C3H8O3)
- 15. To measure the anglesUse the protractor paper provided. Place the semi circle dish on the top “half” of the protractor. Line up the laser with the angle of incidence. Record the angle of refraction.
- 16. Closure QuestionsHow does the index of refraction of corn oil compare to air? How does the index of refraction of corn oil compare to water?
- 17. Closure QuestionsHow does the index of refraction of corn oil compare to Pyrex® (n=1.474)?
- 18. Closure QuestionsWhat factors might change the index of refraction of a solution of 95% methanol in water?
- 19. Closure QuestionsWhat are some ways scientists might use the index of refraction to identify materials?
- 20. Index of Refraction Simulatorhttp://phet.colorado.edu/en/simulation/bending-light