Reflection and Refraction 1 Reflection Reflection is when

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 boundary id e Normal In c nt ra y θi Medium 1 act fr Re θr Medium 2 ray ed 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 • 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

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!

Some Common values for n… Vacuum 1 Fused. Quartz 1. 4585 Crown. Glass 1. 52 Diamond 2. 42 Air 1. 0003 Salt 1. 54 Whale Oil 1. 460 Water 1. 33 Asphalt 1. 635 Lead 2. 6 Ethyl Alcohol 1. 36 Heavy Flint Glass 1. 65

Sample problems 1. 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

• n = c/v • n = 3. 0 x 108 m/s / 2. 0 x 108 m/s • nplastic = 1. 5

2. Find the speed of light in water (n = 1. 33).

• Vwater = 2. 3 x 108 m/s

Snell’s Law • Used to determine the angles of incidence or refraction. • nisin i = nrsin 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 = 1. 0003) hits a sheet of crown glass (n = 1. 52) at 30. 0 , at what angle was it refracted? 10

• nisin i = nrsin r • (1. 0003)sin 30 = (1. 52)sinθ • θ = 19. 21°

4. A ray of light in air is incident upon a diamond at 45. 0 (ndiamond = 2. 42) What is the angle of refraction?

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

• nr = 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 108 m/s