1. Reflection and Refraction1

2. 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

3. Reflection
Boundary
normal
incident ray θ i θ r
reflected ray 3

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

5. Refraction Normal Incident ray θi θr Refracted ray Medium 1 boundary5

6. 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

7. Index of refraction
Measure of how much light bends when it passes into a medium from a vacuum
nsubstance = c / vsubstance
Index of refraction = speed of light in a vacuum speed of light in the medium
c = 3.0 x 108 m/s 7

8. 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.
SO, NO UNITS!

9. 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

10. Sample problems
The speed of light in one type of plastic is 2.00 X 108 m/s. What is the index of refraction of plastic? 8

11. n = c/v
n = 3.0 x 108 m/s / 2.0 x 108 m/s
nplastic = 1.5

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

13. Vwater = 2.3 x 108 m/s

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

15. Sample Problems
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

16. nisini = nrsinr
(1.0003)sin30 = (1.52)sinθ
θ = 19.21°

17. 4. A ray of light in air is incident upon a diamond at 45
4. A ray of light in air is incident upon a diamond at 45.0 (ndiamond = 2.42) What is the angle of refraction?

18. 16.99°

19. Sample Problems
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

20. nr = 2.04

21. Sample Problems
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.

22. 2 steps
Use Snell’s Law and then n = c/v
v = 2.0 x 108 m/s