Chapter 17

Chapter 17Reflection & 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 = 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

c

vsubnsub =

Speed of Light in Other Substances

c

nsubvsub =

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

ni sin i = nr sin r

Snell’s Law

n1 = air n2 = water

i

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(nair = 1.00) & strikes

glass (nglass = 1.52) with an incident angle of 30.0o. Calculate the angle of refraction:

A light ray from air(nair = 1.00) strikes glass

(nglass = 1.61) with an incident angle of 36.9o. Calculate the angle of

refraction:

A light ray from air(nair = 1.00) & strikes

diamond (ndiamd = 2.42) with an incident angle of 45.0o. Calculate the angle of refraction:

A light ray incident from air (nair = 1.00) at

45.0o passes into an unknown substance at

30.0o. 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 90o, 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

Rainbows fallfrom 40 – 42o

from incident

Rainbows

Rainbows fallfrom 40 – 42o

from incident

A light ray from water(nw = 1.33) & strikes

diamond (ndiamd = 2.42) with an incident angle of 53.0o. 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(nw = 1.33) & strikes

glass (nglass = 1.51) with an incident angle of 53.0o. 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 30o from normal.

Calculate: refl & refr