how do these work?. how can peacock feathers create bright colors? why do oil puddles or soap...

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