Transcript The Electromagnetic Spectrum

The Electromagnetic
Spectrum
A Mnemonic Device for the
Waves in the Spectrum
• Rabbits
Mate
In
Very
Unusual
eXpensive
Gardens
(Radio Waves)
(Microwaves)
(Infrared)
(Visible Light)
(Ultraviolet Rays)
(X-Rays)
(Gamma Rays)
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.
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
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
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
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.
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
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.
Weather Radar
Doppler Radar
Weather Radar Picture
Other Uses for Radar
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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
MRI’s
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.
MRI
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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.
MRI’s
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/cancertopics/factsheet/Risk/cellph
ones (look at #6)
http://www.cancer.gov/newscenter/tip-sheet-cancermyths
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
Uses of Infrared
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Remote controls
Heal injuries
Night vision
Thermal imaging
Weather forecasting
To study space- astronomy
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.
Uses for Night Vision
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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.
An image taken from a camera
equipped with night vision
Thermal Imaging
In visible light
As seen with infrared
camera
Used in firefighting
To find victims in smoke filled rooms
And to locate hot spots like
this subsurface fire at a
landfill
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
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
Diagnosis of Injury and Disease
Dangers of Infrared
• Like radio waves infrared photons do not
carry much energy
• Non-ionizing radiation
• Only danger- overheating