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Chapter 16 – Light
What type of wave is light?(last chapter)
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ELECTROMAGNETIC SPECTRUM• Contains only transverse waves• All forms of light are included• EM spectrum usually shown from low
frequency to high frequency– this also means that the wavelength goes
from long to short on the same scale• No medium is required for these waves to
travel
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Radio wave
Micro wave
Infrared (IR)
Visible
ROYGBIV
Ultraviolet (UV)
X-wave Gamma wave
Communication (radio, cell phone, satellite)
Communication
Heat food
Remote control
Thermal imaging
What we see “black light”
Sun
X-ray Large stars
Nuclear reaction
EM Spectrum
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“KINDA NEW” EQUATION
c = c : speed of light
(3x108 m/s)
: wavelength (m)
: frequency (Hz)
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Types of Materials• Opaque:
– material absorbs/reflects all of the light– no light gets through (ex. Brick)
• Translucent:– material absorbs/reflects some of the light– most light gets through (ex.lamp shade)
• Transparent:– material absorbs/reflects none of the light– all light passes through (ex. glass)
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Confusing Vocabulary
• Luminous: an object that emits light• Illuminated: an object that reflects light• Luminous flux []: the rate at which light
is emitted• Lumens (lm): the unit for luminous flux• Illuminance [E]: the amount of light
incident on a surface• Lux (lx): the unit for illuminance
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Illuminance Equation
E =
4 r2
where:E is illuminance (lux)
is luminous flux (lumens)
r is the distance from the source (meters)
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Producing LightIncandescent– A piece of metal in
a closed space is heated by electricity
– Filament (glowing metal) made of tungsten
Fluorescent– An electric current
is sent through a gas (mercury and argon) in a closed space
– Similar to lightning
All artificial producers of light follow one of these two methods. The only exception is a laser.
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COLORS & PIGMENTS OF LIGHT
• Additive color process – all three colors of light have the correct intensities, they appear white.
• Primary colors:.– red
– green
– blue
• Primary Pigments – absorbs only one primary color and reflects two from white light.
– yellow (absorbs blue, reflects red and green)
• Secondary pigments – absorbs two primary colors and reflects one (red, green., and blue)
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Polarization
• Light is a transverse wave that oscillates in more than one direction
• Polarization is when light is forced to choose one particular direction of oscillation (light coming off of a road is reflected and becomes polarized).
• Ex. – polarized sunglasses – keeps the glare off
• Types:
– Vertical and horizontal (most common)
– Clockwise and counterclockwise
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Ch 16 Homework
53. 2 lux54. 3.84x108 m55. 100 Watts57. 1306 lm58. 15,000 km
59. 7.0x10-7 m62. Vertically65. 2.3 m67. 14.7 m68. light takes 5 s,
while sound takes 4.7 s
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