Transcript Frequency and wavelength - UMD Department of Physics

Black-Body Radiation
A black-body is a material which
absorbs any light falling on it.
A black-body also radiates!
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The radiation contains all frequencies, but
is peaked at some n which reflects the
temperature of the object: n ~ T.
A lot of the heated objects radiate like
a blackbody
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The sun, a filament….
Spectrum of Blackbody radiation
at different temperatures
Cosmic Microwave Background
Radiation
A radiation left over when electrons and
nuclei combine into atoms (t=0.3 M
years)

It’s a black-body radiation with T=2.7K and
wavelength 0.2cm!
1% of the static in your radio from this
“cry of the baby universe”!
First discovered by Pezias and Wilson
(1965). Now allows us to see the map
of the baby universe (COBE!)
How to produce light?
Nuclear Reactions (in the sun)
Chemical reactions (burn stuff,
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combustion)
Wood, Coal, Oil, Kerosene, Candle, Natural
Gas ...
Limelight, gas mantle: inorganic salt (1885)
Electric lamps: (burning electricity)
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Arc lamp (charged particles smashing into
electrodes)
Filament lamp & florescent lamp

ARC Lamps
Broadway New York City 1881
Incandescent Filament Lamp
(Patented by Edison in 1880)
“Be courageous! Whatever setbacks America has encountered,
it has always emerged as a stronger and more prosperous nation....
Be brave as your fathers before you. Have faith and go forward!"
Incandescent Filament Lamp
7% efficiency (others gone to heat).
 Higher temp, tungsten filament will
melt.
 Partially vacuumed, filled with argon
and nitrogen, but still the filament
evaporate.
 In tungsten-halogen lamp, filament is
protected with a quartz enclosure.

Tungsten Halogen Lamps:
http://americanhistory.si.edu/lighting/tech/th.htm
Light from discharges
A glass tube is filled with some gas at
high pressure.
Electrodes at the end are connected to
an alternating current source, which
drives the charge first one way and
then the other.
The electric fields pull electrons off the
electrodes, which then collide with
atoms and shake their electrons off.
http://www.goodmart.com/facts/light_bulbs/hid_diagram.aspx
Different types of HID
Metal Halide
Metal Halide lamps offer high efficacy, excellent color rendition, long
service life, and good lumen maintenance. They are used often in
outdoor applications and in commercial interiors, overhead projector,
photoraphy.
Sodium
High pressure sodium lamps are very energy efficient. Mercury and
sodium vapors produce a yellow/orange light with extremely good
lumens per watt performance. Although they tend to render colors
poorly they have an exceptionally long service life, (up to 40,000
hours).
Xenon gas
the latest technology for automobile lighting. You may also hear
it called “Xenon” lights.
Aurora Borealis (northern lights)
Charged particles from the sun strikes the
molecules in the upper atmosphere.
Fluorescent Lamps
Using discharges to produce ultraviolet
radiation (black light) in gas (mercury
vapor)
Using phosphors (flouresces) to absorb
the UV radiation and produce visible
light.

A 40 Watt bulb fluorescent is 4 times more
brighter than a 40 Watt incandescent bulb.
http://home.howstuffworks.com/fluorescent-lamp.htm
Other interesting light Sources
LCD:

http://www.plasma.com/classroom/what_is_tft_lc
d.htm
Plasma
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http://ask.yahoo.com/ask/20030602.html
When an electrical current is applied to a pixel, the
gas reacts to form plasma, which in turn produces
UV light. The light reacts with the colored
phosphors and magically enhances the flat screen
to produce higher-contrast ratios and a better,
more realistic picture.