The Electromagnetic Spectrum

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The Electromagnetic Spectrum
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A Mnemonic Device for the Waves in the Spectrum

• Rabbits (Radio Waves)Mate (Microwaves)In
  (Infrared)Very (Visible Light)Unusual (Ultrav
  iolet Rays)eXpensive (X-Rays)Gardens (Gamma
  Rays)

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Transmits Radio and TV Signals

• Use continuous sine waves to transmit information
  (audio, video, data
• There are literally thousands of different radio
  waves (in the form of sine waves) around you
  right now -- TV broadcasts, AM and FM radio
  broadcasts, police and fire radios, satellite TV
  transmissions, cell phone conversations, GPS
  signals, and so on
• Each different radio signal uses a different sine
  wave frequency, and that is how they are all
  separated.
• Any radio setup has two parts The transmitter
  and the receiver
• The transmitter takes some sort of message (it
  could be the sound of someone's voice, pictures
  for a TV set, data for a radio modem or
  whatever), encodes it onto a sine wave and
  transmits it with radio waves. The receiver
  receives the radio waves and decodes the message
  from the sine wave it receives. Both the
  transmitter and receiver use antennas to radiate
  and capture the radio signal.

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Radio waves

• Have the longest wavelength and the lowest
  frequency (least energy)
• Are used in communications, astronomy, weather
  forecasting, Radar, and microwaves
• Range in wavelength from larger than the earth to
  about 1 mm
• AM radio waves are about 1,000 feet (1,600
  kilometers) in wavelength, while FM radio waves
  are only a few feet in wavelength
• Microwaves are a very short wavelength type of
  radio wave and range in size from 1 mm to 1 m

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• Astronomy
• study astronomical phenomena that are often
  invisible in other portions of the
  electromagnetic spectrum
• observe the Cosmic Microwave Background
  Radiation, by which we study the birth of our
  Universe in the Big Bang
• probe the Dark Ages before the onset of the
  first stars or galaxies, and study the earliest
  generation of galaxies
• analyze and explore the black holes that live at
  the hearts of most galaxies.
• Since radio waves penetrate dust, scientists use
  radio astronomy techniques to study regions that
  cannot be seen in visible light, such as the
  dust-shrouded environments where stars and
  planets are born, and the center of our Galaxy,
  the Milky Way
• allow astronomers to trace the location, density,
  and motion of the hydrogen gas that constitutes
  three-fourths of the ordinary matter in the
  Universe

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Microwaves Used in Astronomy

• Cosmic Background Explorer (COBE) image of the
  cosmic microwave background, the pink and blue
  colors showing the tiny fluctuations in it

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Cell Phones A cell phone uses one radio frequency
for talking and a second, separate frequency for
listening allowing both people on the call to
talk at once. The carrier chops up the city into
cells. Each cell is usually about 10 square miles
(26 square kilometers). Each cell has a base
station that consists of a tower and a small
building containing the radio equipment. The
radio equipment picks up the radio waves sent by
your phone and relays them to the person you are
talking to. Conversely it radios their response
to you. All cell phones have special codes
associated with them. These codes are used to
identify the phone, the phone's owner and the
service provider.
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Microwave Ovens

• A microwave oven uses microwaves to heat food.
• Microwaves are short wavelength radio waves. The
  longer microwaves close to a foot in length, are
  the waves which heat our food in a microwave
  oven.
• Radio waves in this frequency are absorbed by
  water, fats and sugars. When they are absorbed
  they are converted directly into atomic motion --
  heat.
• These waves are not absorbed by most plastics,
  glass or ceramics allowing heating of the food
  rather than the container

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Weather Forecasting

• Radio waves are sent from an antenna.
• Objects in the air, such as raindrops, snow
  crystals, hailstones or even insects and dust,
  scatter or reflect some of the radio waves back
  to the antenna.
• All weather radars, including Doppler,
  electronically convert the reflected radio waves
  into pictures showing the location and intensity
  of precipitation.
• Doppler radars also measure the frequency change
  in returning radio waves.
• Waves reflected by something moving away from the
  antenna change to a lower frequency, while waves
  from an object moving toward the antenna change
  to a higher frequency.
• The computer that's a part of a Doppler radar
  uses the frequency changes to show directions and
  speeds of the winds blowing around the raindrops,
  insects and other objects that reflected the
  radio waves.

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Weather Radar
Doppler Radar
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Weather Radar Picture
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Other Uses for Radar

• Militarily to detect objects at a long-range
• For missile guidance
• To detect migration patterns of birds/insects
• For air traffic control and navigation
• By police to determine the speed of cars
• This is how it works
• http//science.howstuffworks.com/radar2.htm

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MRIs Magnetic Resonance Imaging

• Are used to create images of inside of body
  without harmful ionizing radiation
• Allows for detailed imaging of soft tissues which
  can be used to detect disease or injury . In
  addition scientists have used MRI images of the
  brain to study how the brain works.

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MRI

• uses radio waves that interact with protons (the
  nuclei of hydrogen atoms)
• the radio signals are repeatedly turned on and
  off
• Energy in the radio waves is absorbed by
  different atoms in the target area and reflected
  back out of the body.
• When the radio waves are reflected off the
  patient's body, they generate new signals that
  are detected by the MRI machine
• These signals are sent to a MRI computer, which
  also collects all the signals from the giant
  coil, then combined to create the 3-D images.

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MRIs
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Dangers of Radio Waves

• Since they have a low frequency, they do not
  carry much energy
• Non-ionizing radiation
• Investigations into cell phones and microwaves
  causing cancer
• No definitive studies http//www.cancer.gov/cancer
  topics/factsheet/Risk/cellphones (look at 6)
• http//www.cancer.gov/newscenter/tip-sheet-can
  cer-myths

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Infrared Light

• Invisible to the eye but can be detected as
  warmth on the skin
• Divided into three regions near infrared
  (nearest the visible spectrum), with wavelengths
  0.78 to about 2.5 microns (a micron, is 10-6
  metre) middle infrared, with wavelengths 2.5 to
  about 50 micrometres and far infrared, with
  wavelengths 50 to 1,000 micrometres

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Uses of Infrared

• Remote controls
• Heal injuries
• Night vision
• Thermal imaging
• Weather forecasting
• To study space- astronomy

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Night Vision

• Night vision can work in two very different ways,
  depending on the technology used.
• Image enhancement - This works by collecting the
  tiny amounts of light, including the lower
  portion of the infrared light spectrum, that are
  present but may be imperceptible to our eyes, and
  amplifying it to the point that we can easily
  observe the image.
• Thermal imaging - This technology operates by
  capturing the upper portion of the infrared light
  spectrum, which is emitted as heat by objects
  instead of simply reflected as light. Hotter
  objects, such as warm bodies, emit more of this
  light than cooler objects like trees or
  buildings.

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Uses for Night Vision

• The original purpose of night vision was to
  locate enemy targets at night. It is still used
  extensively by the military for that purpose, as
  well as for navigation, surveillance and
  targeting. Police and security often use both
  thermal-imaging and image-enhancement technology,
  particularly for surveillance. Hunters and nature
  enthusiasts use NVDs to maneuver through the
  woods at night.
• Detectives and private investigators use night
  vision to watch people they are assigned to
  track. Many businesses have permanently-mounted
  cameras equipped with night vision to monitor the
  surroundings.
• A really amazing ability of thermal imaging is
  that it reveals whether an area has been
  disturbed -- it can show that the ground has been
  dug up to bury something, even if there is no
  obvious sign to the naked eye. Law enforcement
  has used this to discover items that have been
  hidden by criminals, including money, drugs and
  bodies. Also, recent changes to areas such as
  walls can be seen using thermal imaging, which
  has provided important clues in several cases.

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An image taken from a camera equipped with night
vision
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Thermal Imaging
In visible light
As seen with infrared camera
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Used in firefighting
To find victims in smoke filled rooms
And to locate hot spots like this subsurface fire
at a landfill
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Used in Astronomy
Infrared light penetrates dust better allowing us
to find new stars, galaxies, asteroids and
quasars. Also allows us to study cool stars that
do not give off much visible light.
Visible light
With infrared
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Planetary nebulae are actually the remains of
stars that once looked a lot like our sun. When
sun-like stars die, they puff out their outer
gaseous layers. These layers are heated by the
hot core of the dead star, called a white dwarf,
and shine with infrared and visible-light colors.
Our own sun will blossom into a planetary nebula
when it dies in about five billion years. In
Spitzer's infrared view of the Helix nebula, the
eye looks more like that of a green monster's.
Infrared light from the outer gaseous layers is
represented in blues and greens. The white dwarf
is visible as a tiny white dot in the center of
the picture. The red color in the middle of the
eye denotes the final layers of gas blown out
when the star died
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Diagnosis of Injury and Disease
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Dangers of Infrared

• Like radio waves infrared photons do not carry
  much energy
• Non-ionizing radiation
• Only danger- overheating