Chapter 17 Reflection Refraction Reflection When light rays

Chapter 17 Reflection & Refraction

Reflection • When light rays bounce back off of a medium boundary

Refraction • The bending of light rays when passing from one medium to another

Ray • A straight line path representing the direction of a light wave

Specular Reflection • Reflection off of a smooth surface which results in reflected wave that are parallel

Specular Reflection • Produce good images • Mirrors give regular reflections

Diffuse Reflection • Reflection off of a rough surface which results in reflected waves that are not parallel

Diffuse Reflection • Because light waves are scattered all over the place, no image can be seen

Law of Reflection • The angle of reflection equals the angle of incidence

Law of Reflection a b b = a Normal

Optical Density • How fast light passes through a substance as compared to the speed of light in a vacuum.

Optical Density • As optical density increases, the speed in which light passes decreases

Index of Refraction (n) • Ratio of the speed of light in a vacuum to the speed of light in a material

Indices of Refraction • Vacuum: n = 1. 00 • Air: n = 1. 0003 • Water: n = 1. 33 • Ethanol: n = 1. 36

Indices of Refraction • Crown glass: n = 1. 52 • Quartz: n = 1. 54 • Flint glass: n = 1. 61 • Diamond: n = 2. 42

Speed of Light in Other Substances nsub = c vsub

Speed of Light in Other Substances vsub = c nsub

Solve for the speed of light in each of the following: water (n = 1. 33) crown glass (n = 1. 52) diamond (n = 2. 42)

Solve for the speed of light in a substance with an optical density of 1. 50:

Snell’s Law • The ratio of the sine of the angle of incidence over the sine of the angle of refraction is constant for any substance

Snell’s Law n = sin ai sin ar

Snell’s Law ni sin ai = nr sin ar

Snell’s Law ai n 1 = air ar n 2 = water

Draw a model with a light ray passing from one medium to another more optically dense medium. Include reflection & refraction

A light ray from air (nair = 1. 00) strikes glass (nglass = 1. 52) with an o incident angle of 30. 0. Calculate the angle of refraction:

A light ray from air (nair = 1. 00) strikes glass (nglass = 1. 61) with an o incident angle of 36. 9. Calculate the angle of refraction:

A light ray from air (nair = 1. 00) & strikes diamond (ndiamd = 2. 42) with an incident angle o of 45. 0. Calculate the angle of refraction:

A light ray incident from air (nair = 1. 00) at o 45. 0 passes into an unknown substance at o 30. 0. Calculate its index of refraction:

Total Internal Reflection • When light passes from a more optically dense substance to a less optically dense one, the angle of refraction > the angle of incident

b a

Total Internal Reflection (TIR) • When the angle of o refraction 90 , total internal reflection occurs.

Calculate the angles where TIR occurs when light passes from the following to air: water (n = 1. 33) crown glass (n = 1. 52) diamond (n = 2. 42)

Applications & Effects • Prisms • Fiber Optics • Mirages • Red Sunsets • Rainbows

Prisms • When light pass through a prism the various wavelengths of light are dispersed or separated into a spectrum

Prisms

Fiber Optics • A light wave can pass through a thin glass thread surrounded by a reflective substance. Even if the glass thread is bent, the wave passes through as it reflects off the sides.

Mirages • Light refracted from a far away source looks closer

Mirages

Sunsets & Rises • Sunlight is refracted as it strikes the atmosphere at great angles bending light towards Earth

Sunsets • Because different wavelengths are refracted differently, colors change

Sunsets

Rainbows • Sunlight is refracted & reflected by rain droplets dispersing the light into a spectrum

Rainbows

Rainbows fall o from 40 – 42 from incident

Rainbows fall o from 40 – 42 from incident

A light ray from water (nw = 1. 33) & strikes diamond (ndiamd = 2. 42) with an incident angle o of 53. 0. Calculate the angle of refraction:

A light ray from water (nw = 1. 33) & strikes glass (nglass = 1. 51) with an incident angle of o 53. 0. Calculate the angle of refraction:

Calculate the angle of total internal reflection of pukon with n = 3. 00

An incident ray from air strikes quartz (n = 1. 50) at an angle of o 30 from normal. Calculate: refl & refr