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12.4 The Index of Refraction

12.4 The Index of Refraction. The Index of Refraction (n). The ratio of the speed of light in a vacuum ( c ) to the speed of light in a medium ( v ) Note : Since light is fastest in a vacuum, the following is true:. Relationship between angles and index of refraction.

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12.4 The Index of Refraction

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  1. 12.4 The Index of Refraction

  2. The Index of Refraction (n) • The ratio of the speed of light in a vacuum (c) to the speed of light in a medium (v) • Note: Since light is fastest in a vacuum, the following is true:

  3. Relationship between angles and index of refraction • We can relate n to the angle of incidence (i) and the angle of refraction (R):

  4. Sample problems • The speed of light in glycerol is 2.04 x 108 m/s. Calculate the index of refraction for glycerol. • The index of refraction for quartz is 1.46. Calculate the speed of light in quartz.

  5. The Speed of Light • The speed of light in a vacuum (ie. in the absence of any material) is c = 3.00 × 108 m/s • The speed of light is different for each medium, but is always less than the speed of light in a vacuum. • The change in speed of light at the boundary of a substance causes refraction. • The speed of light in a medium is a distinctive property of that medium.

  6. The Speed of Light • The index of refraction for a particular material is defined as the ratio of the speed of light in vacuum to the speed of light in that material. where n is the index of refraction where c is the speed of light in a vacuum where v is the speed of light in the material • Because c and v are both speeds, their units cancel out and n is a dimensionless unit. See table 1 on page 524 for index of refraction for various media.

  7. The Index of Refraction • Lets try calculating the index of refraction! Example 1: The speed of light is sodium chloride is 1.96 X 108 m/s. Calculate the index of refraction for sodium chloride. • Given n = ? c = 3.00 × 108 m/s v = 1.96 X 108 m/s n= 3.00 × 108 m/s 1.96 X 108 m/s n= 1.53 Therefore, the index of refraction for sodium chloride is 1.53. • The formula: n = c can be rearranged to solve for the speed of light v • v * see sample problem 2 on page 525

  8. The Speed of Light Things to note: • The speed of light in any material is always smaller than c. • The index of refraction of a material is always greater than 1. • Practice: page 525 # 2-8, 10

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