Transcript Electromagnetic Radiation … aka Light

Electromagnetic Radiation
… aka Light
The EM spectrum
•Not just the “light” we can see…
•Ranges from low frequency radio waves to high frequency x-rays
•Small window of frequencies called “visible light”
Light Properties: Review
• Electromagnetic radiation travels
________________in
3.00 E8 m/s a vacuum
– or about 186,000miles/second
• This velocity has a symbol of? c
• Travels in rays… straight line from an origin.
Visible Light
• A small slice of the EM spectrum can be
detected by human eyes.
• Color is the brains code for the frequency of
perceived light.
• Roy G. Biv – acronym
• On the left are low frequencies and long
wavelengths. On the right are high frequencies
and short wavelengths
R
O
Y
G
B
I
V
Color # 1- Rules for Color
• White is ALL colors of the VS (visible spectrum)
Color # 1- Rules for Color
• Black is the absence of all colors.
• Black appears black because
nothing is reflected from it…
therefore the light energy is
turned to heat!
Color # 1- Rules for Color
• Objects of a particular color
absorb all other colors except for
the color they “normally” appear.
• Ex. Green plants absorb all colors
(roybiv) and use these energy
frequencies to produce sugar
during photosynthesis…, except
green… they reflect green.
Color # 2- Rules for Color
• An object’s color depends SOLELY on the
color of light that is reflected off of it.
Object looks green
Color # 3- Rules for Color
• An object’s color depends SOLELY on the
color of light that is reflected off of it.
No light is reflected, no
light reaches the eye, so
object appears black!
The turtle absorbed
red light
Velocity of light through other
materials – Snell’s Law
• When light travels through
substances, its velocity is
effected.
• The amount the speed is reduced
is the optical density (n)
• n = c / velocity in the substance
Find the v of each of these.
n = c/v
Material
n
Vacuum
1.0000
3.00
E8
m/s
Air
1.0003
3.00
E8
m/s
Ice
1.31
2.29
E8
m/s
Water
1.333
2.25
E8
m/s
Ethyl Alcohol
1.36
2.21
E8
m/s
Crown Glass
1.52
1.97
E8
m/s
Zircon
1.923
1.56
E8
m/s
Diamond
2.417
1.24
E8
m/s
Law of Reflection
• Establish “normal” – an imaginary
perpendicular line to the surface of a
reflective object.
normal
Θi = Θr
Angle of
incidence
Angle of
reflection
mirror
Inverted images
• Mirrors produce images which have an
“apparent distance” equal to that of the real
object is from the mirror.
• Images are also “inverted”
• Mirrors need not be the same size as the object
to produce a full sized image.
d
d
Mirrors and Reflection
• Light rays travel in parallel rays from a
source to an object that reflects them.
• A reflection can be “diffuse”, “perfect”,
or “focused”
• Mirrors create either perfect (specular)
or focused reflections depending on
their shape.
Diffuse Reflection
• The rays are scattered in different directions.
This is the way we see most objects in
everyday life.
Perfect (specular) reflection
• Plane mirrors create perfect parallel reflection of
rays.
mirror
Focused reflection
• Concave and Convex Mirrors create
focused reflections. They still obey the
Law of Reflection.
• Convex
Concave
Focal
point
Mirrors and Reflection #4
enlarged
Multiple normals,
resulting in slightly
different reflected
angles
Refraction
• High frequencies are more affected by this
phenomenon.
• Snell’s Law also predicts how much it will be bent in
the equation…
ni sinΘi =nrsinΘr
• n = optical density or Index of refraction.
Refraction#1
When light changes the material in which it
travels, changes in velocity cause a change in
direction. The θincidence is different than the
θrefracted.
Refraction#2
Optical
density low
Optical
density high
Optical
density low
Optical density of the
material determines
amount of “bending”
parallel
High O.D. = small Θ
Low O.D. = larger Θ
air
water
Virtual fish
Actual fish
Lenses
• Lenses obey Snell’s Law by refracting light to a
certain degree.
• Lens shape has the biggest effect on light
behavior.
• Two types :
Concave
Convex
Renaissance Masters - Tracers???