How do these work?

How can peacock feathers create bright colors?

Why do oil puddles or soap bubbles have colors?

When light (or sound) enters a new medium,

the wave can be:

1/___________________ back into the original medium;

2/ __________________ at the boundary; or,

3/____________________into the new medium

medium 1

medium 2

boundary

incidentray

reflectedray

transmittedray

energy absorbed(boundary heats)

Which wave (ray) has the most energy?

Which has the greatest amplitude?

reflectedabsorbed

transmitted

incident

incident

When light passes into a denser medium, it__________________.

c = 3.0 x 108 m/sa/ In vacuum:

b/ In water:

c/ In glass:

molecules

c c c c

Light is________________, then _______________from each molecule. _____________ molecules, it travels at aspeed______________.

c c c c c c c

Higher density __________________________________________

slows down

v = ___________________

absorbed emittedBetween

v = c

more interactionsslower speed

Ex. Light passing from air into glass : ________________

air(medium 1)

glass(medium 2)

boundary

incidentray

vglass < vair

Characteristics of the incident ray:

vi _______________________________

fi _______________________________

i _______________________________

Ai _______________________________

determined by medium

colorfound from = v/f

energy in wave

vr

fr

r

Ar

= vi, b/c it is in the same medium

= fi, b/c it’s the same color

= i, b/c = v/f

air(medium 1)

glass(medium 2)

boundary

incidentray

reflectedray

< Ai, b/c not all energy is reflected

Characteristics of the reflected ray:

v2

f2

2

A2

= fi, b/c it’s the same color

< v1 (given)

i, b/c = v/f

Characteristics of the transmitted ray:

< A1 b/c not all energy is transmitted

air(medium 1)

glass(medium 2)

boundary

incident ray

reflected ray

transmitted ray

Notice: fr, fi, and f2 are ___________________________!!!exactly the same

Water

When you put your hand

in water…

Does it look like this… or this?

In the new medium, the speed _____________ and

frequency_________________________ , so the wavelength

must ________________________ .

Different materials slow the __________________ by

different amounts. How much it slows is summed up

in a quantity called the ______________________________

n, of a material. It is defined as the ratio of the speed

of light _______________________ to the speed of light

__________________________:

"n" is called the ___________________ index because

"slowing down" can cause light to ______________ (bend).

Notice that n _______________________ because it is the

______________________________________________________ .

n = c/v

absolute index of refraction ,

in a vacuum, c,in the material, v

changes

remains the samealso change

speed of light

refractive

refract

has no unitsratio of two speeds, and the units cancel.

Physics Reference Tables, page 5, top:

Page 2, bottom:

Note:This tableis really onlytrue for yellowlight, and onlyapproximatelytrue for otherfrequencies

Ex: Determine the speed of (yellow) light in water.

n = c / v

Given: nwater = 1.33

c = 3.00 x 108 m/s

Unknown: v = ?

1.33 = (3.00 x 108 m/s) / v

v = 2.26 x 108 m/s

To compare the speeds and wavelengths of two materials, use the equation:

higher n __________________

__________________

slower speed

shorter wavelength

n2

n1 v2

v1

2

1= =

Ex: what is the relationship between v and n?

vn = c / v

n

Physics Reference Tables, page 5, top:

Ex: The wavelength of a certainlaser in air is 780. nm. A CD is coated with a plastic material that has an absolute index of refraction of 1.55. Find the wavelength of the light in the CD

n2

n1 2v2

v1 1= =

1.55

1.00 2

780. nm=

n1

n2

air

CD

laser

Given:

2 = ?

1 = 780. nm

n1 = 1.00

n2 = 1.55

Unknown:

2 = 780. nm/1.55

2 = 503 nm

Ex: Laser light entering a CD:

shorter can read more data