Transcript Light & Colors Chapters 27 & 28

Test Review for
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Light is created by vibrating charged particles
It is a transverse wave
It is the only wave that does not need a
medium to travel through.
Time the appearance of the following image:
Symbol is c
3 x 108 m/s or
 300,000,000 m/s
 A constant (when in a vacuum or atmosphere)
 Average speed of light slows down in different
materials due to time delays between
absorption and re-emission within the material
(you won’t need to know how to calculate this).
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Stop your whining!
Same equations as the last unit
v=d/t
v=λf
This time though, replace the v with c!
c=d/t
c=λf
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It takes sunlight 8 minutes to travel to Earth.
How far away is the sun?
First convert 8 minutes to seconds
 8 minutes x 60 seconds/minute = 480 seconds
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Now plug this into d=ct
 d=3x108 m/s x 4.8x102 s
 d=1.44 x 1011 m (144 million kilometers)
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What is the frequency of violet light with a
wavelength of 400 nm (4 x 10-7 m)?
Rewrite c=λf to f = c/λ
f = (3x108 m/s) / (4x10-7m)
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7.5 x 1014 Hz
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Created by OPAQUE objects blocking light.
Umbra: dark center, all light is blocked
Penumbra: fuzzy edges, some light is blocked
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Technical (read fancy) name for all light,
including visible light.
All EM-waves travel at the same speed
They are defined by their different
frequencies and wavelengths.
Increasing frequency 
Decreasing wavelength 
Increasing energy 
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Objects can be opaque to some EM waves
but translucent to others.
Windows:
 Can you see through them?
 Can you get sunburned
through one?
 Can infrared pass through them? (Look at the
glasses above)
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If you double your distance from the light:
The illuminance of the light is quartered.
If you triple your distance from the light:
The illuminance of the light will be 1/9th of the
original brightness
If you halve your distance from the light:
The illuminance of the light is quadrupled.
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Illuminance ~ 1/distance2
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Natural light is randomly polarized.
Polarizers block light waves oscillating in one
direction.
 Reduces brightness of light by 50% for the first
polarizer.
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Second polarizer at 90o of first polarizer will
block all light.
Reflected light/glare
are horizontally
polarized
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Primary colors - red, blue, green
White objects reflect all light.
Black objects absorb all light.
Blue objects reflect BLUE light
and absorb all other light.
All other light colors are made of the three
primary colors.
Complementary colors: the two colors that can
be added together to make white light.
Use of additive colors:
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Depends on colored light being subtracted.
Primary colors: magenta,
cyan, and yellow.
Absorb one primary color of
light and reflects two.
Filters subtract all light except
for the color of the filter.
Pigments/dyes absorb all
colors except for the few they reflect.
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A red shirt under magenta light: red
A green book under blue light: black
Used by: