LIGHT
Principles of Physics

Waves created by fluctuating electric and magnetic
fields
Transverse waves
 Can travel in a vacuum – do not need a medium
 Travel at the speed of light in a vacuum
(c = 300,000,000 m/s)


Organized by frequency and wavelength

http://www.phy.ntnu.edu.tw/ntnujava/index
.php?topic=35
3.84x1014 Hz
4.82x1014 Hz
Red
5.03x1014 Hz
Orange
5.20x1014 Hz
Yellow
6.10x1014 Hz
Green
6.59x1014 Hz
Blue
7.69x1014 Hz
Violet
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Longest wavelength and lowest frequency
RADIO WAVES ARE NOT SOUND WAVES
Provide the signal for communications devices
such as: radios, television, cell phones
Micro waves are used to cook food
Infrared waves are used for TV remote
controls, night vision

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Shortest wavelength, highest frequency
Cause damage to human cells because
wavelength is close to atomic size
Ultraviolet – sun bathing
X – used to detect bone damage, baggage
screening at airports
Gamma – radioactive decay

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Waves that allow us to see color
Red – longest wavelength, lowest frequency
(3.84 x 1014 Hz = 384,000,000,000,000 Hz)
Violet – smallest wavelength, highest frequency
(7.69 x 1014 Hz = 769,000,000,000,000 Hz)
Light Sources
 Emit light waves
 Produce light
 Sun, light bulbs, flames
Illuminated Objects
 Most objects
 Actually are reflecting light
 People, plants, rocks, etc.
Moon – source or illuminated?

Intensity (brightness) = amplitude
Large amplitude, a lot of
energy (very hot)
Small amplitude, less
energy (warm)

Color = frequency


Order of colors = spectrum
Primary colors of light – red, green and blue
 Red light +green light +blue light = white light
 Different than pigment colors (ink, paint, etc)
 These reflect light, they are not sources
Mixing colors Applet
Light can be reflected or
transmitted:
Materials
 Transparent – transmit
clearly (clear glass, still
water)
 Translucent – transmit blurry
(frosted glass)
 Opaque – no transmission
(light may be reflected or
absorbed)
Speed of light in a vacuum
=c
= 299,792,458 m/s
= 2.99792458 x 108 m/s
≈ 3.00 x 108 m/s
Speed of light in any other material depends on optical
density (ability of a material to transmit light)

Greater optical density, more light slows down
Air
c / 1.003 ≈ 3.00 x 108 m/s
Water
c/1.33
Diamond c/2.42
1.
2.
3.
Put a decimal after the first
non-zero number and drop
any zeroes
Determine the power of ten
by counting the places
before of after the decimal
Show the places before or
after the decimal using an
exponent. Use a negative on
your exponent if the decimal
is before the number
1. Ex:
300,000,000 → 3.0
0.000345 → 3.45
2. Ex:
300,000,000 → 3.0
8 places after
0.000345 → 3.45
4 places before
3.
Ex: 300,000,000 →
3.0 x108
0.000345 →
3.45 x 10-4