Reflection and Refraction 1

Reflection Reflection is when light hits a boundary and bounces off The law of reflection states that the angle of incidence is equal to the angle of reflection 2

Reflection 3

Refraction Refraction is the change in direction of waves crossing a boundary between two different media Angle would be measured with a protractor! 4

Refraction Incident ray Refracted ray Normal θiθi θrθr Medium 1 Medium 2 boundary 5

Parts of a refraction diagram Normal – line drawn at a right angle to the barrier between the media Boundary – barrier between the media Angle of incidence – angle of ray in first media Angle of refraction – angle of ray in second media 6

Index of refraction Measure of how much light bends when it passes into a medium from a vacuum n substance = c / v substance Index of refraction = speed of light in a vacuum speed of light in the medium c = 3.0 x 10 8 m/s 7

If you didn’t get that… index of refraction = noun Optics. a number indicating the speed of light in a given medium as the ratio of the speed of light in a vacuum to that in the given medium Symbol: n Also called index, refractive index. indexrefractive index. SO, NO UNITS!

Some Common values for n… Vacuum 1 CrownGlass 1.52 Air Salt 1.54 Water 1.33 Asphalt Ethyl Alcohol 1.36 Heavy Flint Glass 1.65 FusedQuartz Diamond 2.42 Whale Oil Lead 2.6

Sample problems 1.The speed of light in one type of plastic is 2.00 X 10 8 m/s. What is the index of refraction of plastic? 8

n = c/v n = 3.0 x 10 8 m/s / 2.0 x 10 8 m/s n plastic = 1.5

2. Find the speed of light in water (n = 1.33).

V water = 2.3 x 10 8 m/s

Snell’s Law Used to determine the angles of incidence or refraction. n i sin  i = n r sin  r Index of refraction of 1 st medium x sine of angle of incidence = Index of refraction of 2 nd medium x sine of angle of refraction 9

Sample Problems 3.If a light beam in air (n = ) hits a sheet of crown glass (n = 1.52) at 30.0 , at what angle was it refracted? 10

n i sin  i = n r sin  r (1.0003)sin30 = (1.52)sin θ θ = 19.21°

4. A ray of light in air is incident upon a diamond at 45.0  (n diamond = 2.42) What is the angle of refraction?

16.99°

Sample Problems 5.A ray of light passing through ethyl alcohol (n = 1.36) strikes a solid at an angle of 75º. If the angle of refraction is 40º, what is the index of refraction of the solid? 11

n r = 2.04

Sample Problems 6.Find the speed of light in a substance if the ray of light enters the substance from air at an angle of 75º to the surface and the angle of refraction is 80º to the surface.

2 steps Use Snell’s Law and then n = c/v v = 2.0 x 10 8 m/s