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Electromagnetic Waves &
the Electromagnetic Spectrum
Electricity can be
static, like what
holds a balloon to
the wall or makes
your hair stand on
end.
Magnetism can also
be static like a
refrigerator
magnet.
But when they change
or move together,
they make waves electromagnetic
waves.
Electromagnetic waves
Formed when an electric
field (blue arrows)
couples with a magnetic
field (red arrows).
The magnetic and electric
fields of an em wave
are perpendicular to
each other and to the
direction of the wave.
Electromagnetic Waves
• Transverse waves without a medium!
• (They can travel through empty space)
• They travel as vibrations in
electrical and magnetic fields.
– Have some magnetic and some
electrical properties to them.
When an electric field changes, so does the
magnetic field. The changing magnetic field
causes the electric field to change. When one
field vibrates—so does the other.
RESULT-An electromagnetic wave.
Electromagnetic waves travel VERY
FAST – around 300,000
kilometres per second (the speed
of light).
At this speed they
can go around the
world 8 times in one
second.
Waves or Particles?
• Electromagnetic radiation has properties of
waves but also can be thought of as a stream
of particles.
– Example: Light
•
Light as a wave: Light behaves as a transverse
wave which we can filter using polarized lenses.
•
Light as particles (photons): When directed at a
substance light can knock electrons off of a
substance (Photoelectric effect)
Electromagnetic Spectrum—name for the
range of electromagnetic waves when
placed in order of increasing frequency
RADIO
WAVES
INFRARED
RAYS
MICROWAVES
ULTRAVIOLET
RAYS
VISIBLE LIGHT
GAMMA
RAYS
X-RAYS
Notice the wavelength is
long (Radio waves) and gets shorter (Gamma Rays)
Ionizing Radiation
vs
Non-ionizing Radiation
Ionizing
– radiation that is
strong enough to
damage molecules and
cells
– includes the higher
frequency forms of
UV radiation, all Xradiation and all
gamma radiation
Non-ionizing
– includes the lower
frequency forms of UV
radiation, and all forms
of radiation “below”
(visible, IR, microwave,
and radio wave
radiation).
Background radiation: Low levels
of radiation from both natural and
man-made sources that is always
around us.
Natural background
radiation examples
– gamma radiation that
penetrates our
atmosphere from
outer space
– radiation released
from rocks, soil, and
water.
Man-made sources of
radiation
– fallout from nuclear
weapons testing
– radiation released
into the environment
from coal-burning
and nuclear power
plants.
RADIO WAVES
Have the longest
wavelengths and
lowest
frequencies of
all the
electromagnetic
waves.
Global Positioning Systems (GPS) measure the
time it takes a radio wave to travel from
several satellites to the receiver, determining
the distance to each satellite.
A radio picks up radio waves through an
antenna and converts it to sound waves.
– Each radio station in an area broadcasts at a
different frequency.
• # on radio dial tells frequency.
MRI
(MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a
magnet to create an image.
MICROWAVES
Have the
shortest
wavelengths and
the highest
frequency of
the radio
waves.
Used in microwave
ovens.
• Waves transfer
energy to the
water in the food
causing them to
vibrate which in
turn transfers
energy in the
form of heat to
the food.
RADAR
(Radio Detection and
Ranging)
• Used to find the
speed of an object
by sending out radio
waves and measuring
the time it takes
them to return.
INFRARED RAYS
Infrared= below red
Shorter wavelength
and higher frequency
than microwaves.
A remote control uses light waves just
beyond the visible spectrum of light—
infrared light waves—to change channels
on your TV.
You can feel the
longest ones as
warmth on your
skin
Warm objects
give off more
heat energy than
cool objects.
Thermogram—a picture that shows regions of different
temperatures in the body. Temperatures are calculated by
the amount of infrared radiation given off.
Therefore people give
off infrared rays.
Heat lamps give off
infrared waves.
VISIBLE LIGHT
Shorter wavelength and
higher frequency than
infrared rays.
Electromagnetic waves we
can see.
Longest wavelength= red
light
Shortest wavelength=
violet (purple) light
ULTRAVIOLET RAYS
Shorter
wavelength and
higher
frequency than
visible light
Carry more
energy than
visible light
UV Waves are Invisible to
the Human Eye
Bees, along with some
birds, reptiles and
other insects, can
see near-ultraviolet
light reflecting off
of plants.
Bug zappers attract
insects with
ultraviolet light to
lure them to the
trap.
ULTRAVIOLET ASTRONOMY
AURORAE
X- RAYS
Shorter
wavelength and
higher
frequency than
UV-rays
Carry a great
amount of
energy
Can penetrate
most matter.
Bones and teeth absorb x-rays. (The light part
of an x-ray image indicates a place where the xray was absorbed)
Too much exposure
can cause cancer
(lead vest at
dentist protects
organs from
unnecessary
exposure)
Used by engineers
to check for tiny
cracks in
structures.
– The rays pass
through the
cracks and the
cracks appear
dark on film.
GAMMA RAYS
Shorter wavelength
and higher frequency
than X-rays
Carry the greatest
amount of energy
and penetrate the
most.
SOURCES OF GAMMA RAYS
Produced by the hottest and most energetic
objects in the universe
– neutron stars and pulsars
– supernova explosions
– regions around black holes
On Earth - generated by nuclear explosions,
lightning, and the less dramatic activity of
radioactive decay.
Exploding
nuclear
weapons emit
gamma rays.
Gamma Rays in Medicine
They are able to penetrate most materials and aren't
easily blocked.
When they pass through matter, they eject electrons
from the atoms they collide with.
– This is called ionization, and it's dangerous to
living cells; prolonged gamma radiation can lead to
grave illness and even death.
Yet we use gamma rays from cobalt-60 for cancer
treatment.
We also use gamma rays in industry to test castings
and welded joints for tiny, almost invisible cracks or
defects.
Used in radiation treatment to kill
cancer cells.
Can be very harmful if not used
correctly.
The Incredible
Hulk was the
victim of
gamma
radiation.
Gamma Knife surgery
> 200 beams of gamma radiation are directed at
small tumors
– causing 90 to 95 % of them to cease growing
and a majority of them to shrink
– malignant and benign tumors and Parkinson's
disease.
PET (Positron Emission Tomography) scan
– patient is injected with a radioactive
substance and placed on a table that slides into
a gamma ray detector.
– Doctors can then track blood flow and other
biochemical processes within the body
International Security and Food
Safety
Container Security Initiative
By 2008, 58 ports worldwide were equipped with
X-ray and gamma ray screening devices, giving
security officers access to 86 percent of all
maritime cargo in containers
“Irradiation pasteurization" or “cold pasteurization”
– passing food through a beam of gamma rays
– kills bacteria that could spoil food or render it
poisonous
– food that is irradiated today does not become
radioactive itself, and is considered safe.
Why are Gamma Rays More
Harmful than Radio Waves?
In Conclusion…
• All forms of electromagnetic radiation have important
applications and uses
• Exposure to non-ionizing radiation (lower frequency)
forms of EMR is relatively harmless
• Exposure to ordinary forms and amounts of radiation
is not harmful (you have been exposed to all forms of
EMR every day of your life)
• Among those forms to which we should limit our
exposure, there are important and helpful uses
• We can harvest the energy in the electromagnetic
radiation from the sun to produce power
Continued SUMMARY
All electromagnetic waves travel at the same
speed. (300,000,000 meters/second) in a
vacuum.
• They all have different wavelengths and
different frequencies.
– Long wavelength-lowest frequency
– Short wavelength highest frequency
– The higher the frequency the higher the
energy.
•