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Refraction

Refraction. Light and Geometric Optics. What is Refraction?. Refraction is the bending of light as it travels, at an angle , from a material with one refractive index to a material with a different refractive index. Image formation by refraction on a curved surface.

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Refraction

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  1. Refraction Light and Geometric Optics

  2. What is Refraction? Refraction is the bending of light as it travels, at an angle, from a material with one refractive index to a material with a different refractive index

  3. Image formation by refraction on a curved surface

  4. Fermat’s Principle when light travels from one point to another, it follows the path that will take the least time. Pierre de Fermat (1601-1665), French mathematician and physical theorist.

  5. Describing Refraction Using Rays refracted ray the ray that is bent upon entering a second medium angle of refraction the angle between the normal and a refracted ray

  6. Refraction

  7. Refraction - example Refraction can be seen when looking into the glass of water. Air has a refractive index of about 1.0003, and water has a refractive index of about 1.33. If a person looks at the straw, which is placed at a slant, partially in the water, the object appears to bend at the water's surface.

  8. Index of Refraction • is the ratio of the speed of light in a vacuum to the speed of light in a given medium. • Index of Refraction: n = c v where n is the index of refraction c is the speed of light in a vacuum v is the speed of light in a medium

  9. Index of refraction of water is in a given medium n = speed of light in a vacuum speed of light in water = 3.00 × 1 08 m/s 2.26 × 108 m/s = 1.33

  10. Apparent Image Formation: DepthThe image of an extended object is distorted.

  11. Table 1: Indices of RefractionGases/Liquids Substance Index of Refraction (n) Vacuum 1.000 00 Gases at 0°C and 101.3 kPa Hydrogen 1.000 14 Oxygen 1.000 27 Air 1.000 29 Carbon dioxide 1.000 45 Liquids at 20°C Water 1.333 Ethyl alcohol 1.362 Glycerol 1.470 Carbon disulfide 1.632

  12. Table 2: Indices of RefractionSolids Substance Index of Refraction (n) Solids at 20°C Quartz (fused) 1.46 Plexiglas™ or Lucite™ 1.51 Glass (crown) 1.52 Sodium chloride 1.54 Glass (crystal) 1.54 Ruby 1.54 Glass (flint) 1.65 Zircon 1.92 Diamond 2.42

  13. Practice Problems 1. Calculate the speed of light in flint glass. 2. Calculate the speed of light in crown glass. 3. a. The speed of light in a solid is 1.24 × 108 m/s. Calculate the index of refraction. b. Use the solids Table 2 to identify the substance. 4. The speed of light in a sample of glass is 1.9 × 108 m/s. What is the refractive index of this glass? 5. The speed of light through a material is 1.24 × 108 m/s. What material is this? 6. The speed of light in quartz is 2.1 × 108 m/s. What is the index of refraction? 7. What is the speed of light through alcohol? 8. What is the speed of light through sapphire? (n=1.77) Use the GRASP method of calculation.

  14. Snell’s Law The phenomenon of refraction was first stated mathematically in 1621 by the Dutch astronomer and mathematician Willebrord Snell

  15. Problems using Snell’s LAW When light passes from the air into water at an angle of 60o from the normal, what is the angle of refraction? G: n1 (air) = 1.00 sin Θ2 = 0.6511 n2 (water) = 1.33 Θ2 = 40.62 angle of incidence Θ1 = 60o P: Therefore, the angle of refraction is 41o R:Θ2 = ? A: n1sin Θ1 = n2sin Θ2 S: sin Θ2= n1sin Θ1 n2 = 1.00 x sin (60o) 1.33 = 1.00 x 0.8660/1.33

  16. Problems using Snell’s LAW When light passes from air into water at an angle of 30o from the normal, what is the angle of refraction?(22o) When light passes from air into alcohol at an angle of 45o from the normal what is the angle of refraction? When light passes from water into diamond at an angle of 600 from the normal what is the angle of refraction? The refractive index of the lens in a human eye is 1.41. If a ray of light goes from air into the lens at an angle of 55.5o, what is the angle of refraction?(35.5o) A ray of light approaches a jar of honey at an angle of 30o. If the angle of refraction is 19.5o, what is the refractive index of honey?(1.5)

  17. Dispersion Dispersion is the refraction of light into separate wavelengths, or colours. The most common type of dispersion is the formation of a rainbow. Fig. 1: Dispersion of light in prism – visible light spectrum ROY G BIV (Mnemonic to remember Red, Orange, Yellow, Green, Blue, Indigo, Violet)

  18. Dispersion Fig. 2: Dispersion of light in a gemstone

  19. Homework Read pgs. 449-456, do the practice problems on pg. 455 and answer question #1-8 on page 456.

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