The
Electromagnetic
Spectrum
April 3, 20007
So far we have talked about
Mechanical Waves……
but there are some waves that don’t
need a medium to travel through…
Microwaves
Radio
Larger Waves
Infrared
Visible
X-Ray
Ultraviolet
Gamma
Smaller Waves
We call these Electromagnetic
waves (such as light) that travel
throughout “matter-less” space.
Light vs. Sound
• Transverse
wave
•Does not require
a medium
•Frequency tells
you the color
•Amplitude
tells you the
brightness
•Longitudinal
wave
•Requires a
medium
•Frequency tells
you the pitch
•Amplitude tells
you the loudness
(decibels)
300,000 km/s (fast!)
**As far as we know, NOTHING
travels faster than the speed of
light!!
•Very fast compared to
the speed of sound
(.340 km/s)
Spectrum: the full range, in this case,
the full range of light waves that can be
given off by excited electrons.
•Arranges light waves based on their
wavelength and frequency
Long wavelength = Low frequency
Short wavelength = High frequency
•ALL
electromagnetic
waves travel at
the same
SPEED
Frequency Increases & Wavelength Decreases!
1. RADIO WAVES
Lowest frequency and longest
wavelength; used for
communication.
•Very LONG wavelengths
•Radio and TV waves are
regulated by the FCC
(Federal Communications
Commission) to reduce
interference
Just
FYI!!
•AM Radio waves have a longer wavelength
(lower frequency)
•FM Radio waves have a shorter wavelength
(higher frequency)
A higher energy radio wave;
used for cooking food
Just
FYI!!
Water and fat absorb energy carried
by microwaves
When these molecules move
around faster they get hotter and
give off heat
Microwaves are absorbed by
molecules up to 2 cm below the
surface (this is why food is
sometimes cold in the middle! YUK!)
Just
FYI!!
•Used in radar because it
penetrates rain and fog
•Used by Cell phones
• Does not occur naturally and is
made by various forms of
communication technology
•SETI = Search for extraterrestrial
Intelligence uses this frequency to
search, because it is not made
naturally
2. INFRARED WAVES
Can’t be seen, but can be felt as
heat.
Everything gives off
infrared radiation; it
depends on the
thermal energy
•Examples of
Infrared
waves:
TV's
remote
control
Fire
Radiators
Infrared film to
photograph a house to
reveal areas in the
structure that are leaking
and wasting heat
Infrared light is
even used to heat
food sometimes special lamps that
emit thermal infrared
waves are often used
in fast food
restaurants!
Just
FYI!!
•Primary source of Infrared Radiation is heat
or thermal radiation
Just
Any object that has a temp. radiates in FYI!!
the infrared, even ice cubes
Ex. Charcoal is not burning but will emit heat
• How Infrared radiation is used:
– Snakes in the ‘viper’ family have sensory
“pits” that detect I.R., so they can detect
warm-blooded prey
– Infrared pictures can be taken using
special cameras and film that detects
differences in temperature
• Once the pictures are taken, they assign
different brightness or false colors to
Just them to provide a picture our eyes can
FYI!! interpret
3. VISIBLE LIGHT
Part of the spectrum you CAN
see.
ROYGBIV
The color of visible light depends
on its frequency
4. Ultraviolet Light (UV)
Present in sunlight and have
enough energy to kill living cells
•Invisible to the
human eye
UV Light is used:
In Tanning beds
•Some insects, like
bumblebees, can see To sterilize
them
surgical equipment
In Food
processing
Just
FYI!!
•Ozone absorbs highest
energy UV light
•UV Light can cause
sunburns and
eventually malignant
melanomas
5. X-Rays
•Enough energy to pass
through most materials
(skin)
• Lead is one
material that X –
Rays cannot pass
through
•X-rays were first observed and
documented in 1895 by Wilhelm
Conrad Roentgen, a German
scientist
•He found them quite by accident
when experimenting with vacuum
tubes.
•Also can be created by a
machine like those for
medical x-rays
Just
FYI!!
Just
FYI!!
•Originate in nature
deep in space in the
hot nebulae of stars
•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
Just
FYI!!
•bones and teeth are dense and absorb more X-rays
then your skin does
•silhouettes of your bones or teeth are left on the X-ray
film while your skin appears transparent
When X-ray light shines on us, it goes through
our skin, but allows shadows of our bones to be
projected onto and captured by film
•Metal absorbs even more X-rays - can you see the
filling in the image of the tooth
6. Gamma Rays
Has the Highest energy of all
of the electromagnetic waves
Emitted by radioactive
materials
Used to treat cancer,
Can go through concrete!
•Smallest wavelengths and possess
more energy than any other wave in
the electromagnetic spectrum
Produced by the hottest regions
of the universe
•They are produced by:
violent events as supernova explosions or the
destruction of atoms
The decay of radioactive material in space
Neutron stars and pulsars, and black holes Just
 radioactive atoms and nuclear explosions
FYI!!
•Medical Uses:
Radioactive Tracers (put into a patients
body and followed as it goes through)
A patient with lung problems can
breathe in Xenon-133, a gas that emits
gamma rays
A special camera is used to take Just
FYI!!
pictures
The patient isn’t injured by the
radiation because they quickly breathe
out all the gas
Radiotherapy
Treatment of cancer