The Electromagnetic Spectrum
Why are roses red and violets blue?
 Why is the rainbow ROYGBIV?
 What causes sunburn?
 How fast is a speeding text?
 X-rays?
 What makes a remote control work?
 What makes FM and AM different?
 Is there really x ray vision?
 What if we could see heat?

What is it?
The electromagnetic spectrum is the
complete spectrum or continuum of light
including radio waves, infrared, visible light,
ultraviolet light, X-rays and gamma rays
 An electromagnetic wave consists of electric
and magnetic fields which vibrate, thus
making waves.

Wavelength and Frequency
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For any kind of wave
there exists a simple
relationship between
wavelength and
frequency.
The wavelength is
measured as the
distance between two
successive crests in a
wave.
The frequency is the
number of wave crests
that pass a given point
in space each second.
Let’s Talk Frequency!
C = λν
The
frequency (v) of a wave is
the number of waves to cross a
point in 1 second (units are Hertz –
cycles/sec or sec-1)
λ
is the wavelength- the distance
from crest to crest on a wave
The
product of wavelength and
frequency always equals the
speed of light.
C = λν
Why
does this make sense?
 NOTE:
c is a constant value= 3.00 x 108 m/s
Waves
Properties of waves include speed, frequency
and wavelength
 Speed (s), frequency (f) and wavelength (l) are
related in the formula l x f = s
 All light travels at a speed of 3 x 108 m/s in a
vacuum

The speed of light!

The speed of light is
the same for all seven
forms of light.

It is 300,000
kilometers per second
or 186,000 miles per
second.
Wavelength, Frequency and
Energy
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Since all light travels at the same speed,
wavelength and frequency have an indirect
relationship.
Light with a short wavelength will have a high
frequency
Light with a long wavelength will have a low
frequency.
Light with short wavelengths has high energy
Light with long wavelengths has low energy
The Electromagnetic
Spectrum
Radio Waves - communication
 Microwaves – radar, weather
prediction
 Infrared - “heat waves”
 Visible Light - detected by your eyes
 Ultraviolet - causes sunburns
 X-rays - penetrates tissue
 Gamma Rays - most energetic

Radio waves
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Low energy waves with
long wavelengths
Includes FM, AM, radar
and TV waves
Low frequency
Used in many devices
such as remote control
items, cell phones,
wireless devices, etc.
MRI of the Brain
Radio
(Low Frequency & Very High Frequency)
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Emitted by
– Astronomical Objects
– Radio Station
transmitters
Detected by
– Ground based radio
telescopes
– Radios
– By studying the radio
waves originating
from planets, comets,
nebula astronomers
can learn about their
composition,
structure, and
motion.
Microwaves

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Longer than radio, shorter than light and infrared
First used in radar, now used in communication,
medicine and consumer use
Practical use for microwaves- besides mac
and cheese!
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Radar is an acronym for
"radio detection and
ranging".
Radar was developed to
detect objects and
determine their range (or
position) by transmitting
short bursts of
microwaves.
The strength and origin
of "echoes" received from
objects that were hit by
the microwaves is then
recorded.
Infrared waves
Invisible electromagnetic
waves that are detected as
heat
 Can be detected with special
devices such as night goggles
 Used in heat lamps and remote
controls
 Higher energy than
microwaves but lower than
visible light.
 In what situations might you
see infrared as heat?

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How do we use infrared to view
objects in space?
Infrared
(Near and Thermal)

Emitted by
– Sun and stars (Near)
– TV Remote Controls
– Food Warming Lights
(Thermal)
– Everything at room
temp or above

Detected by
– Infrared Cameras
– TVs, VCRs,
– Your skin
Night vision
22
Visible Light
The portion of the electromagnetic spectrum
that human eyes can detect
 ROY G BIV (red, orange, yellow, green, blue,
indigo, violet)
 Red is the lowest frequency and violet is the
highest frequency
 Why is the rainbow arranged this way? (think
length of wavelengths.)

 The
colors we see in objects are the
colors that are reflected, all other colors
are absorbed. A red t-shirt appears red
because red is reflected to our eyes and
the other colors are absorbed.
 When all colors are being reflected we see
white light (white isn’t really a color)
Herschel’s Experiment

Herschel’s Experiment
– Discovered Invisible
Light
– In 1800, Herschel
places his control
thermometer just
outside the red end
of the spectrum
– Result: The outside
thermometer
registered the
highest temperature
Ultraviolet
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Ultraviolet (UV) light has
shorter wavelengths than
visible light.
Though these waves are
invisible to the human eye,
some insects, like bumblebees,
can see them
Emitted by
–
–
–
–
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Tanning booths (A)
The sun (A)
Black light bulbs (B)
UV lamps
Detected by
– Space based UV detectors
– UV Cameras
– Flying insects (flies)
X-Rays
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High energy waves
When you get an X-ray taken
at the hospital, X-ray
sensitive film is put on one
side of your body, and X-rays
are shot through you.
Because your bones are
dense and absorb more Xrays then your skin does,
dark silhouettes of your
bones are left on the X-ray
film while your skin appears
transparent
Used in medicine, industry
and astronomy
Can cause cancer
Chandra X-ray Observatory
Chandra is designed to
observe X-rays from
high energy regions of
the universe, such as
the remnants of
exploded stars.
 The most sophisticated
observatory built to
date.
 Deployed by the Space
Shuttle Columbia on
July 23, 1999,

Chandra X-ray
Observatory
Gamma rays
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Photons with energies billions
of times greater than visible
light.
Blocked from Earth’s surface
by the atmosphere.
Occur naturally from stellar
objects like neutron (dead)
stars
Gamma-ray bursts (from dead
or dying stars) can release
more energy in 10 seconds
than the Sun will emit in its
entire 10 billion-year lifetime!
Gamma rays are also man
made for use in medicine
EM Spectrum in Astronomy
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If we could only observe in visible light, our
knowledge of the universe would be greatly
limited

By looking at objects at different
wavelengths, we get a different view and lots
more information

Some objects are only visible at certain
wavelengths
The Sun at Different Wavelengths
Visible
X-ray
Ultraviolet
X-ray
Using the EM waves to
view galaxies
Animation—View a Galaxy at
different wavelengths
Viewing other astronomical
objects- what makes each
different?
Brief SUMMARY
A. All electromagnetic waves travel at the
same speed. (300,000,000 meters/second in
a vacuum.
B. They all have different wavelength and
different frequencies.
•Long wavelength-lowest frequency
•Short wavelength highest frequency
•The higher the frequency the higher the
energy.
•Checkpoint- interactive!
The following diagram shows the
electromagnetic spectrum. However all the
names and colours have been mixed up.
INFRA-RED
X -RAYS
ULTRAVIOLET
GAMMA
RAYS
RADIO
WAVES
MICRO
WAVES
mixed up diagram!
What region of the REAL electromagnetic spectrum
1.___ has the highest frequency?
2.___ has the longest wavelength?
3.___ has the most energy?
4.____ is used in remote controls for televisions?
5. ____can be used to kill cancer cells?
6.____ is used to make florescent inks ‘glow’?
37
Time to think…..

1. What is the relationship
between frequency and
wavelength?
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2. What is meant by ‘spectrum’?
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3. What does ROY G BIV mean?
Now, let’s really think
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4. Can you actually see x-rays?
– Support your answer.
5. Which color is more energetic, red
or yellow?
 6. Which type of wave travels faster,
gamma or radio?
 7. Why are microwaves more
dangerous than radio waves?
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Think about it….

You have just been
involved in a traffic
incident that leaves you
stranded on the side of
the road. Which part of
the electromagnetic
spectrum would be of the
most use to you and why?
Atoms and Light
 The
movement of electrons inside of
atoms produces light and other
electromagnetic radiation.
 Sunlight produces every color in the
rainbow but…
 Each element gives off only certain
frequencies of light, called spectral lines.
In effect each element has its own
signature of spectral lines allowing us to
identify which element we have or what
stars are made of.
Below is a picture of the spectral lines
given off by hydrogen. Note there are 3
different frequencies.
 The
emission spectra makes it
possible to identify inaccessible
substances. Most of our knowledge of
the universe comes from studying the
emission spectra of stars.
 Below is the spectra of a few more
elements.
Helium
 Neon
 Argon
 In
a star, there are many elements
present. The way we can tell which are
there is to look at the spectrum of the
star.
 From spectral lines astronomers can
determine not only the element, but the
temperature and density of that element
in the star
 Emission lines can also tell us about the
magnetic field of the star. The width of
the line can tell us how fast the material
is moving
 If
the lines shift back and forth, it
means that the star may be orbiting
another star - the spectrum will give
the information to estimate the mass
and size of the star system and the
companion star.
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Around a compact object (black hole,
neutron star), the material is heated to
the point it gives off X-rays, and the
material falls onto the black hole or
neutron star. By looking at the spectrum
of X-rays being emitted by that object and
its surrounding disk, we can learn about
these objects.
Examples from Space!
Think about it….

You have just been
involved in a traffic
incident that leaves you
stranded on the side of
the road. Which part of
the electromagnetic
spectrum would be of the
most use to you and why?
Answers
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1. Frequency and wavelength are properties of waves and
since speed is constant for em waves, as frequency
increases, wavelength decreases.
2. Spectrum is a continuum of all electromagnetic waves
3, ROY G BIV is the difference colors of the visible light
in order of longest wavelength to shortest wavelength.
4. X-rays can not be seen, only the waves in the visible
light portion are visible.
5. Yellow is higher energy than red because it has a
shorter wavelength and higher frequency.
6. Both travel at the same speed, 300,000 km/s (all em
waves travel at the same speed)
7. Microwaves have a higher frequency than radio and
carry more energy.