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The Electromagnetic
Spectrum
Notes
What Is An
Electromagnetic
Wave?
• An electromagnetic (EM) wave consists
of vibrating electric and magnetic fields
that move through space at the speed
of light.
• An EM wave is a transverse wave that
carries electrical and magnetic energy.
The energy is EM radiation. Light is an
example of and EM wave.
What Is An Electromagnetic
Wave?
• EM waves do not need a medium to travel
•
through. They can travel though empty
space (vacuum). For example, sunlight
travels through empty space to reach
Earth.
Light and all other EM waves are produced
by charged particles. Charged particles
have an electric field surrounding them.
When a charged particle moves, it
produces a magnetic field. Thus, a moving
charged particle is both electric AND
magnetic.
What Is An
Electromagnetic
Wave?
• All EM waves travel at the same speed.
In a vacuum, they travel at about
300,000 km/s or 186,000 miles/s. This
is known as the speed of light.
• At this speed, light from the sun takes
8.3 minutes to travel the 150 million
kilometers to Earth.
•
•
What is the EM
Spectrum?
All EM waves travel at the same speed in
a vacuum, but they have different
wavelengths (λ) and different frequencies
(f). The EM spectrum is made up of radio
waves, microwaves, infrared (IR), visible
light, ultraviolet (UV) light, X-rays, and
gamma rays.
The EM spectrum is the complete range of
EM waves. The waves are placed in order
of increasing f. As the frequencies of the
waves get higher, their λ get shorter.
What is the EM
Spectrum?
• At one end of the EM spectrum are radio
waves. Radio waves have low frequencies
and long wavelengths. At the other end of the
spectrum are gamma rays. Gamma rays have
high f and short λ.
• The higher the frequency of the EM waves,
the more energy they have. The farther up the
spectrum you go, the more harmful the waves
become to humans. Gamma waves have the
highest frequency, so they have the most
energy, and therefore cause the most harm to
humans.
Radio Waves
• Radio waves are at one end of the EM
spectrum.
• Radio waves are EM waves with the
lowest frequencies and longest
wavelengths.
• Radio waves with the very lowest f are
used to carry signals for radio and TV
programs.
Infrared
• Infrared rays follow radio waves in the EM
spectrum. Infra- is a prefix meaning “before” or
“below.” So infrared means “below red.”
• Infrared (IR) rays are EM waves with higher
frequencies and shorter wavelengths than radio
waves.
• IR rays have more energy than radio waves
because they have higher f. You can feel the
energy of IR rays as heat. heat lamps give off
infrared rays.
Infrared
• Most objects give off some IR rays. You
can use an infrared camera to see
objects in the dark. These cameras take
pictures called thermograms.
Visible Light
•
•
•
Visible light follows infrared rays in the EM
spectrum.
EM waves that you can see are called
visible light. Visible light has higher f and
shorter λ than infrared rays.
All colors of light visible have wavelengths
that fall between 390 nm (3.9x10-7 m) and
750 nm (7.5x10-7m). Anything with
wavelengths outside of this range, humans
beings cannot see directly.
Visible Light
•
We see different wavelengths of visible light as
different colors. When all colors combine, we see
white light. A prism has the ability to diffract white
light into its seven parts. From shortest to longest λ,
the colors of visible light are ROY G BIV.







Red
Orange
Yellow
Green
Blue
Indigo
Violet
Ultraviolet Rays
•
•
•
•
Ultraviolet (UV) rays follow visible light in the
EM spectrum.
UV rays are EM waves with higher frequencies
and shorter wavelengths than visible light.
UV rays have more energy than visible light
because they have higher frequencies.
UV rays help our bodies make vitamin D.
However, too much UV radiation can cause
sunburn, damage your eyes, and cause skin
cancer.
X-Rays
•
•
•
•
X-rays follow UV rays in the EM spectrum.
X-rays are EM waves with higher frequencies and
shorter wavelengths than UV rays.
X-rays have more energy than UV rays because they
have higher f. X-rays have enough energy to pass
through many materials, including skin and other soft
tissues.
Even though X-rays are used to take pictures of teeth
and bones, and - in engineering - industrial materials,
too much exposure can cause serious health issues
including cancer.
Gamma Rays
•
•
•
•
•
Gamma rays follow X-rays in the EM spectrum.
Gamma rays are EM waves with the highest
frequencies and shortest wavelengths.
Gamma rays have more energy than any other type of
EM wave. Gamma rays have enough energy to pass
through most materials.
Some gamma rays can be used to kill cancer, or to
examine internal structures of the body.
Some objects in space give off gamma rays. Special
telescopes can detect these gamma rays.
Types of Telescope
• Telescopes are instruments that collect and
focus light and other forms of EM radiation.
• A telescope that collects and focuses visible
light is called an optical telescope. The two
major types of optical telescopes are
refracting telescopes and reflecting
telescopes.
Types of Telescopes
• A radio telescope is a device used to
collect radio waves that come from objects is
space. Most radio telescopes have large,
curved surfaces like dishes.
• Radio telescopes can combine multiple
dishes to form one larger dish.
The Very Large Array
(VLA) in New Mexico is a
set of 27 radio telescopes
that can be maneuvered
and combine together to
form one radio telescope
25 kilometers in diameter.
The Arecibo radio telescope
in Puerto Rico was built into
a natural bowl in the ground.
It is 305 meters in diameter
and is the largest single
radio telescope in existence.
Types of Telescopes
• Telescopes have also been developed to
look at all parts of the EM spectrum.
• Telescopes can now see into the infrared,
microwave, X-ray, ultraviolet, and Gamma
rays of the EM spectrum.