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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