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

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

Regular 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 incident

Law of Reflection     =   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 = 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 c v sub n sub =

Speed of Light in Other Substances c n sub v sub =

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 sin  i sin  r n =

Snell’s Law n i sin  i = n r sin  r

Snell’s Law n 1 = air n 2 = water ii rr

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 (n air = 1.00) & strikes glass (n glass = 1.52) with an incident angle of 30.0 o. Calculate the angle of refraction:

A light ray from air (n air = 1.00) strikes glass (n glass = 1.61) with an incident angle of 36.9 o. Calculate the angle of refraction:

A light ray from air (n air = 1.00) & strikes diamond (n diamd = 2.42) with an incident angle of 45.0 o. Calculate the angle of refraction:

A light ray incident from air (n air = 1.00) at 45.0 o passes into an unknown substance at 30.0 o. 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

 

Total Internal Reflection (TIR) When the angle of refraction  90 o, 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 from 40 – 42 o from incident

Rainbows Rainbows fall from 40 – 42 o from incident

A light ray from water (n w = 1.33) & strikes diamond (n diamd = 2.42) with an incident angle of 53.0 o. Calculate the angle of refraction:

Answer the questions at the end of Chapter 16

Answer the questions at the end of Chapter 17

A light ray from water (n w = 1.33) & strikes glass (n glass = 1.51) with an incident angle of 53.0 o. 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 30 o from normal. Calculate:  refl &  refr