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Electromagnetic Waves have different wavelengths.
http://science.hq.nasa.gov/kids/imagers/ems/waves3.html
| When
you listen to the radio, watch TV, or cook dinner in a microwave
oven, you are using electromagnetic waves. |
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| Radio waves,
television waves, and microwaves are all types of
electromagnetic waves. They only differ from each other in
wavelength. Wavelength is the distance between one wave crest to
the next. |
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Waves in the electromagnetic spectrum vary in size from very long
radio waves the size of buildings, to very short gamma-rays smaller than
the size of the nucleus of an atom.
Did you know that electromagnetic waves can not only be described by
their wavelength, but also by their energy and frequency? All three of
these things are related to each other mathematically.
This means that it is correct to talk about the energy of an X-ray or
the wavelength of a microwave or the frequency of a radio wave.
The electromagnetic spectrum includes, from longest wavelength to
shortest: radio waves, microwaves, infrared, optical, ultraviolet,
X-rays, and gamma-rays.
Radio Waves
| Radio waves have
the longest wavelengths in the electromagnetic spectrum. These
waves can be longer than a football field or as short as a
football. Radio waves do more than just bring music to your
radio. They also carry signals for your television and cellular
phones. |
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The antennae on
your television set receive the signal, in the form of
electromagnetic waves, that is broadcasted from the television
station. It is displayed on your television screen.
Cable companies have antennae or dishes which receive waves
broadcasted from your local TV stations. The signal is then sent
through a cable to your house.
Why are car antennae about the same size as TV antennae? |
| Cellular phones
also use radio waves to transmit information. These waves are
much smaller that TV and FM radio waves.
Why are antennae on cell phones smaller than antennae on your
radio? |
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Microwaves
| Microwaves have
wavelengths that can be measured in centimeters! The longer
microwaves, those closer to a foot in length, are the waves
which heat our food in a microwave oven. |
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| Microwaves are
good for transmitting information from one place to another
because microwave energy can penetrate haze, light rain and
snow, clouds, and smoke.
Shorter microwaves are used in remote sensing. These
microwaves are used for radar like the doppler radar used in
weather forecasts. Microwaves, used for radar, are just a few
inches long. |
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This microwave tower can transmit information like telephone calls
and computer data from one city to another.
The Infrared
Infrared light lies between the visible and microwave portions of
the electromagnetic spectrum. Infrared light has a range of wavelengths,
just like visible light has wavelengths that range from red light to
violet. "Near infrared" light is closest in wavelength to visible light
and "far infrared" is closer to the microwave region of the
electromagnetic spectrum. The longer, far infrared wavelengths are about
the size of a pin head and the shorter, near infrared ones are the size
of cells, or are microscopic.
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Far infrared
waves are thermal. In other words, we experience this type of
infrared radiation every day in the form of heat! The heat that
we feel from sunlight, a fire, a radiator or a warm sidewalk is
infrared. The temperature-sensitive nerve endings in our skin
can detect the difference between inside body temperature and
outside skin temperature. |
Infrared light is even used to heat food sometimes - special lamps
that emit thermal infrared waves are often used in fast food
restaurants!
| Shorter, near
infrared waves are not hot at all - in fact you cannot even feel
them. These shorter wavelengths are the ones used by your TV's
remote control. |
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Visible Light Waves
Visible light waves are the only electromagnetic waves we can see. We
see these waves as the colors of the rainbow. Each color has a different
wavelength. Red has the longest wavelength and violet has the shortest
wavelength. When all the waves are seen together, they make white light.
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When white light
shines through a prism or through water vapor like this rainbow,
the white light is broken apart into the colors of the visible
light spectrum |
Ultraviolet Waves
| Ultraviolet (UV)
light has shorter wavelengths than visible light. Though these
waves are invisible to the human eye, some insects, like
bumblebees, can see them! (Image of the bumblebee is courtesty
of Mark Cassino.) |
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Scientists have divided the ultraviolet part of the spectrum into
three regions: the near ultraviolet, the far ultraviolet, and the
extreme ultraviolet. The three regions are distinguished by how
energetic the ultraviolet radiation is, and by the "wavelength" of the
ultraviolet light, which is related to energy.
The near ultraviolet, abbreviated NUV, is the light closest to
optical or visible light. The extreme ultraviolet, abbreviated EUV, is
the ultraviolet light closest to X-rays, and is the most energetic of
the three types. The far ultraviolet, abbreviated FUV, lies between the
near and extreme ultraviolet regions. It is the least explored of the
three regions.
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Our Sun emits
light at all the different wavelengths in electromagnetic
spectrum, but it is ultraviolet waves that are responsible for
causing our sunburns. To the left is an image of the Sun taken
at an Extreme Ultraviolet wavelength - 171 Angstroms to be
exact. (An Angstrom is a unit length equal to 10-10
meters.) This image was taken by a satellite named SOHO and it
shows what the Sun looked like on April 24, 2000. |
Though some ultraviolet waves from the Sun penetrate Earth's
atmosphere, most of them are blocked from entering by various gases like
Ozone. Some days, more ultraviolet waves get through our atmosphere.
Scientists have developed a UV index to help people protect themselves
from these harmful ultraviolet waves.
X-rays
As the wavelengths of light decrease, they increase in energy. X-rays
have smaller wavelengths and therefore higher energy than ultraviolet
waves. We usually talk about X-rays in terms of their energy rather than
wavelength. This is partially because X-rays have very small
wavelengths. It is also because X-ray light tends to act more like a
particle than a wave. X-ray detectors collect actual photons of X-ray
light - which is very different from the radio telescopes that have
large dishes designed to focus radio waves!
X-rays were first observed and documented in 1895 by Wilhelm Conrad
Roentgen, a German scientist who found them quite by accident when
experimenting with vacuum tubes.
| A week later, he
took an X-ray photograph of his wife's hand which clearly
revealed her wedding ring and her bones. The photograph
electrified the general public and aroused great scientific
interest in the new form of radiation. Roentgen called it "X" to
indicate it was an unknown type of radiation. The name stuck,
although (over Roentgen's objections), many of his colleagues
suggested calling them Roentgen rays. They are still
occasionally referred to as Roentgen rays in German-speaking
countries. |
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The Earth's atmosphere is thick enough that virtually no X-rays are
able to penetrate from outer space all the way to the Earth's surface.
This is good for us but also bad for astronomy - we have to put X-ray
telescopes and detectors on satellites! We cannot do X-ray astronomy
from the ground.
Gamma-rays
Gamma-rays have the smallest wavelengths and the most energy of any
other wave in the electromagnetic spectrum. These waves are generated by
radioactive atoms and in nuclear explosions. Gamma-rays can kill living
cells, a fact which medicine uses to its advantage, using gamma-rays to
kill cancerous cells.
Gamma-rays travel to us across vast distances of the universe, only
to be absorbed by the Earth's atmosphere. Different wavelengths of light
penetrate the Earth's atmosphere to different depths. Instruments aboard
high-altitude balloons and satellites like the Compton Observatory
provide our only view of the gamma-ray sky.
Gamma-rays are the most energetic form of light and are produced by
the hottest regions of the universe. They are also produced by such
violent events as supernova explosions or the destruction of atoms, and
by less dramatic events, such as the decay of radioactive material in
space. Things like supernova explosions (the way massive stars die),
neutron stars and pulsars, and black holes are all sources of celestial
gamma-rays.
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