Download electromagnetic spectrum

ELECTROMAGNETIC SPECTRUM
reflect
Life on Earth is highly dependent on light. Plants need light for the energy to perform
photosynthesis, and animals need plants for oxygen and food. Animals need light to see
their way around. Have you ever stopped to think about what light actually is? Where does
it come from? How does it move from place to place?
The Electromagnetic Spectrum
The light we see on Earth is a type of electromagnetic radiation. (Radiation refers to
energy that spreads out as it travels.) Electromagnetic radiation is energy made up of
special particles called photons. This energy travels faster than anything else known in the
universe: approximately 300,000,000 meters per
second (mps).
There are many different types of electromagnetic
radiation, but all types travel as waves. Scientists
use wavelength to classify electromagnetic waves.
Wavelength is a measurement of the length of
a single wave of energy. As this diagram shows,
wavelength is measured from the trough (or very
bottom) of one wave to the trough of the next wave.
All the different wavelengths of electromagnetic
radiation make up the electromagnetic spectrum. The electromagnetic spectrum includes
radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-Rays,
and gamma rays. The electromagnetic spectrum is usually organized with the different
types of radiation arranged from longest wavelength to shortest.
In this model of the electromagnetic spectrum, longer wavelengths (such as radio waves
and microwaves) are on the left and shorter wavelengths (such as X-Rays and gamma
rays) are on the right.
© 2013-2014 Accelerate Learning - All Rights Reserved
1
ELECTROMAGNETIC SPECTRUM
Regardless of their wavelengths, all types of electromagnetic radiation travel at about the
same speed of 300,000,000 mps. In addition to wave speed and wavelength, electromagnetic
waves can be measured by frequency. Frequency refers to the number of waves that pass a
given point in a given period of time (usually one second). Electromagnetic waves with longer
wavelengths have lower frequencies: in other words, fewer waves pass a given point each
second. Electromagnetic waves with shorter wavelengths have higher frequencies, which
means more waves pass a given point each second.
look out!
Electromagnetic radiation
is made of particles called
photons. However, it is
important to remember that
photons are a special type
of particle. They are not
like other particles you are
familiar with. Unlike protons
and electrons, photons have
no mass. How the energy of
the electromagnetic spectrum
behaves as both particles
and waves simultaneously is
one of the great mysteries of
science.
Visible Light and Color
Visible light is the only part of
the electromagnetic spectrum
humans can see. Visible light
This model of the electromagnetic spectrum shows the
different colors of visible light. Red light waves, which
have the longest wavelengths and lowest frequencies,
are on the left. Violet light waves, which have the shortest
wavelengths and highest frequencies, are on the right.
is radiated as white light, which is made
up of different wavelengths of radiation.
Visible light ranges in wavelength from
about 400–700 nanometers (nm). Each of
these different wavelengths corresponds
to a different color. We see the longest
wavelengths of visible light as red light. We
see the shortest wavelengths as violet light.
A prism separates white light into different
colors.
White light can be separated into different
colors using a special lens called a prism.
When sunlight shines through raindrops,
the raindrops can act as a prism and
create a rainbow.
© 2013-2014 Accelerate Learning - All Rights Reserved
2
ELECTROMAGNETIC SPECTRUM
Studying the Universe Using Visible Light
Most of our knowledge about the universe comes from observations of visible light.
Sometimes we can look directly at an object with our eyes. Sometimes we must use
telescopes to aid our eyes. At other times, a more complex analysis is required. For
example, scientists have discovered the composition of many objects in the universe—
including distant stars—simply by analyzing the visible light these objects emit or reflect.
Scientists have done experiments to determine the colors given off by different elements
when they are burned. By studying the colors given off by a star, scientists can determine
which elements make up that star. This is spectroscopy, the study of the electromagnetic
spectrum to determine an object’s composition.
When scientists look at stars and other distant objects in space, they are actually looking
back in time. Electromagnetic radiation travels faster than anything else in the known
universe. However, it still takes some time for the radiation to travel across the vast
distances of space. Because of this, scientists measure these vast distances in space
using a unit called the light-year. One light-year equals the distance light travels in one
year: about 9.5 trillion kilometers. The closest star to Earth other than the Sun is called
Proxima Centauri. Proxima Centauri is located about 4.2 light-years from Earth. In other
words, light emitted by Proxima Centauri takes 4.2 years to reach Earth. When scientists
look at Proxima Centauri, they are not observing the star as it is now, but rather as it
appeared 4.2 years ago. This means scientists can observe light from across the universe
that was emitted millions or even billions of years ago. They could even look at a star that
no longer exists!
The Doppler Effect
Visible light has provided scientists with much
information about the objects in the universe.
Scientists have also studied visible light to
understand the nature of the universe itself.
A scientist named Edwin Hubble used visible
light to provide evidence that the universe is
expanding. He did this through his observations
of the Doppler effect.
When an object moves toward
you, waves from the object appear
compressed. When an object moves
away from you, waves appear
stretched. This is the Doppler effect.
The Doppler effect describes how wavelengths
of energy shift as objects move. If an object
emitting electromagnetic or sound waves
is moving toward you, the waves become
compressed. In other words, the wavelengths
© 2013-2014 Accelerate Learning - All Rights Reserved
3
ELECTROMAGNETIC SPECTRUM
appear to become smaller. If an object emitting electromagnetic or sound waves is moving
away from you, the waves become stretched. In other words, the wavelengths appear to
become larger.
The Doppler effect causes sounds to increase or decrease in pitch. It also affects
visible light waves. Recall that we see shorter wavelengths as blue light and longer
wavelengths as red light. When a
star is moving toward Earth, the
light waves emitted by the star
become compressed. The shorter
wavelengths cause the star’s light
to appear blue. This phenomenon
is called blueshift. When a star is
moving away from Earth, the light
waves emitted by the star become
stretched. The longer wavelengths
cause the star’s light to appear
red. This phenomenon is called
redshift.
Edwin Hubble noticed that all the
As the object moves away from the man and
galaxies we can see from Earth
toward the woman, it gives off light waves
experience redshift. Therefore, they
(numbered 1–4 in this diagram). Each observer
must be moving away from Earth.
experiences these light waves differently.
If all of the objects in the universe
are moving away from each other,
the universe must be expanding. Not only is the universe expanding, it appears to be
expanding at an increasing rate. Hubble noticed that the farther an object is from Earth, the
more dramatic the redshift appears. In other words, these objects are moving even faster.
By measuring the intensity of a star’s redshift, scientists can determine the speed at which
a star is moving and use this to calculate its distance from Earth.
what do you think?
Humans cannot directly perceive any part of the electromagnetic spectrum other
than visible light. Most of what we know about the universe and the objects in it
comes from the study of visible light. Do you think scientists can use the rest of
the electromagnetic spectrum to study the universe? If so, how do you think this
is possible?
© 2013-2014 Accelerate Learning - All Rights Reserved
4
ELECTROMAGNETIC SPECTRUM
Using High-Energy Electromagnetic Radiation to Study the Universe
When objects burn, they give off visible light. Hotter, more energetic objects and events in
the universe give off high-energy radiation with wavelengths that are shorter than those
of the visible light spectrum. These include ultraviolet radiation, X-Rays, and gamma rays.
Scientists can use special instruments, called remote sensing instruments, to detect this
radiation and study the objects emitting it. For example, ultraviolet radiation can be used
to study very hot areas of the universe, such as the centers of some galaxies where many
stars are clustered together.
X-Rays are given off by extremely hot gases, so they can be used to study events
that are even hotter and more energetic than burning stars. These include supernova
explosions caused by the deaths of old stars. After some
supernova explosions, the extremely dense, hot core of
the dead star remains as a neutron star. Neutron stars
emit X-Rays that scientists can detect and study. After
other supernova explosions, a black hole is created.
Black holes cannot be studied using visible light. This
is because black holes are so dense, not even light
can escape their gravitational pull. However, scientists
can use X-Rays emitted by a supernova explosion to
determine where black holes are likely to be created or
located.
This image shows the
remains of a supernova
explosion. The lighter
areas are X-Rays detected
by a remote sensing
telescope.
Gamma rays have the shortest wavelengths, highest
frequencies, and highest energies of the entire
electromagnetic spectrum. Bursts of energy from the Sun,
called solar flares, generate gamma rays, as do other highenergy events in the universe. High-energy processes on
Earth, such as nuclear power generation, can also emit
gamma radiation.
Using Low-Energy Electromagnetic Radiation to Study the Universe
Scientists can also use the low-energy parts of the electromagnetic spectrum to study
the universe. This low-energy radiation—including radio waves, microwaves, and infrared
radiation—has lower frequencies and longer wavelengths. Special telescopes can pick up
these waves from across the universe, allowing scientists to discover distant objects that
are impossible to detect through higher-energy waves. Some of these objects are hidden
by dust in space. Others are too cool to emit higher-energy waves.
© 2013-2014 Accelerate Learning - All Rights Reserved
5
ELECTROMAGNETIC SPECTRUM
Because all objects give off infrared radiation in
the form of heat, infrared waves are particularly
useful for detecting cooler objects. Special infrared
cameras can even be used to detect objects on
Earth’s surface.
Low-energy waves have even been used to
understand the origin of the entire universe.
The most widely accepted theory to explain the
origin of the universe is the Big Bang theory. The
Special cameras reveal the infraBig Bang theory states that everything in the
red radiation emitted by things,
universe exploded and expanded out of a single
including people!
point during a single event about 13.7 billion
years ago. This massive explosion of energy
and matter must have given off electromagnetic radiation. Scientists have been able
to detect some of this radiation left over from the Big Bang. This is called cosmic
microwave background (CMB) radiation. CMB radiation can be detected everywhere
in the universe, using a special instrument called the Wilkinson Microwave Anisotropy
Probe (WMAP).
The image produced
by WMAP shows
CMB radiation.
Slight differences
in temperature,
represented by different
colors, indicate areas
of the universe with
more or less matter.
Everyday Life: Uses of the Electromagnetic Spectrum
You need visible light to see, but did you know you use other parts of the electromagnetic
spectrum in your everyday life? Every time you use a cell phone or listen to the radio, you
are using radio waves. Radio waves can travel through the air to transmit information, such
as music or a conversation. A microwave oven gets its name because it uses microwave
radiation to energize the atoms that make up your food. This energy heats up cold food.
Doctors and dentists use X-Rays to examine your teeth and bones. X-Rays can pass
through your skin and muscles to create images of your bones and teeth. Sometimes
electromagnetic radiation can hurt you. When you get a sunburn, it is because of ultraviolet
(UV) radiation given off by the Sun. The UV rays can destroy skin cells, causing painful
blisters and, in some cases, cancers.
© 2013-2014 Accelerate Learning - All Rights Reserved
6
ELECTROMAGNETIC SPECTRUM
What do you know?
The electromagnetic spectrum is made up of seven types of radiation of varying
wavelength. In the diagram below, place each type of radiation in order from longest
wavelength to shortest. Then, decide which characteristic in the following box describes
each type of radiation. Write each characteristic beside the appropriate type of
electromagnetic radiation.
Characteristics of Electromagnetic Radiation
• Can be used to transmit information
• Can be used to study supernovae,
across distances
neutron stars, and black holes
• The only part of the electromagnetic
spectrum humans can see
• Emitted by all objects in the form of heat
energy
• Left over from the Big Bang throughout
the universe
• Can be emitted by nuclear power
generation
• Can result in a sunburn
© 2013-2014 Accelerate Learning - All Rights Reserved
7
ELECTROMAGNETIC SPECTRUM
connecting with your child
Exploring the Doppler Effect
To help your child learn more about the
electromagnetic spectrum, try experimenting
with the Doppler effect together. Sound
waves are not a part of the electromagnetic
spectrum. However, they are shifted by
the Doppler effect the same way that
electromagnetic waves are. The unaided
human eye is not capable of directly
observing the Doppler shift of light on Earth,
but the unaided ear can easily detect the
Doppler shift of sound waves.
A sound’s pitch is related to the frequency of
the waves that produce that sound. Sound
waves with higher frequencies produce
sounds with higher pitches, while sound
waves with lower frequencies produce
sounds with lower, deeper pitches. The
Doppler effect creates an apparent shift
in the frequencies of sound waves as
the source of the sound moves toward or
away from an observer. This is easy to
demonstrate at home.
First, experiment with different sounds and
discuss their frequencies with your child.
Try playing notes on a piano or listening
to some music together. Listen to the
different notes, and ask your child to pick
out the sounds that are produced by higherfrequency waves and lower-frequency
waves. Then, experiment with the Doppler
effect by choosing an object that creates
a repetitive sound that has only one pitch.
This can be an alarm clock, a beeping timer,
a cell phone with a repetitive ring tone, or
a portable stereo playing a recording of a
repetitive sound. Have your child stand in
one spot in a wide, open area, preferably
outside. Hold the object producing the
sound, and stand several feet away from
your child. Tell your child to listen carefully
to the sound, paying careful attention to the
pitch. Then, quickly run back and forth past
your child a few times. Instruct your child to
pay attention to the way the pitch changes
as you run back and forth. Discuss the
phenomenon of the changing pitch as the
sound moves closer and farther away.
Here are some questions to discuss with
your child:
• How does the pitch of this sound relate
to the frequency of the sound waves?
• How does the pitch of the sound change
as I move toward you?
• How does the pitch of the sound change
as I move away from you?
• How can you explain this changing
pitch?
• Sound waves are not a part of the
electromagnetic spectrum. How does
this experiment relate to what you have
learned about the electromagnetic
spectrum and the way it is used to study
the universe?
© 2013-2014 Accelerate Learning - All Rights Reserved
8