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Lesson 201:
ELECTROMAGNETIC RADIATION
A lesson about light, energy, and optical illusions.
Fundamental Questions
Attempting to give thorough and reasonable answers to the following questions will help you gauge your level of understanding this lesson.
Students that can confidently answer these questions have mastered the concepts of this lesson.
1.
2.
3.
If you could be turned into light, what kind of light would
you be and why?
Which is more important to life on Earth, the ozone
layer or the sun?
How can a spectroscope be used to identify the gas in
a car headlight?
4.
5.
6.
7.
What is the difference between AM and FM radio
frequencies?
What is more important to you and the universe: energy
or matter?
What color hurts your eyes the most?
How can you be sure that what you see is not an
illusion?
Lesson Objectives
At the end of this lesson, students should have mastered the objectives listed below.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Students gain an understanding for the importance and uniqueness of light in our universe.
Students gain an appreciation for the limitations and biases of human sight.
Students understand that light has both an electric and a magnetic component that move perpendicular to each other.
Students know what the speed of the light is and can convert the speed into different units.
Students recognize that what they see now is actually what the object appeared to be in the past.
Students can describe the characteristics of light: wavelength, frequency, amplitude, speed, and energy.
Students understand that the different forms of light are characterized by their wavelengths.
Students understand the inverse relationship between wavelength and frequency.
Students understand the direct relationship between energy and frequency.
Students can describe the uses for the seven types of light and how they can help or hurt us.
Honors students can state the wavelengths of all forms and colors of light.
Students are familiar with how a prism/spectroscope works and can use a spectroscope to identify a glowing gas.
Students can describe how light is reflected and how a polarizer can cut down on glare.
Students understand that the wavelengths that an object emits are determined by the object's temperature.
Honors students can use Planck's Constant (6.63 × 10-34 J·sec) to calculate the energy of light.
Important Terms
The following terms are some of the vocabulary that students should be familiar with in order to fully master this lesson.
1.
2.
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11.
E = mc2
electromagnetic radiation
electromagnetic spectrum
wavelength
frequency
amplitude
speed of light
c = λf
radio waves
microwaves
infrared
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
visible light
ROY G. BIV
ultraviolet
x-rays
gamma rays
prism
spectroscopy
spectroscope
emission spectra
absorption spectra
continuous spectrum
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
photon
refraction
diffraction
optical
angle if incidence
angle of reflection
polarizer
* Planck's Constant
Hertz
* Joule
Remote Sensing
Assessment Questions
The following are examples of questions that students should be able to answer. These or similar questions are likely to appear on the exam.
1.
2.
3.
What is the speed of light in Km/s and mi/hr?
* Convert the speed of light from kilometers per
second to meters per hour. Show your work.
List all the forms of light from longest wavelength
to shortest.
4.
5.
6.
What are 5 things that all forms of
electromagnetic radiation have in common with
each other?
Why is light called "electromagnetic radiation"?
* How many minutes old is light that comes from
an object that is 40,000,000,000,000 miles away?
1
7.
8.
9.
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11.
12.
13.
14.
* Imagine that you are talking to a friend using
cell phones and the cell phone tower that
receives your signals and transfers them to your
phones is 2 kilometers away from both of you.
You say the word "dongabinkyboo".
Approximately how much time passes before
your friend hears your funny word and laughs?
Why can't you use visible light to "see"
molecules?
List all the forms of light from lowest frequency to
the highest.
List all the forms of light from lowest energy to
the highest.
List the colors of visible light in order from the
lowest energy to the highest.
Describe how wavelength, frequency, and speed
of light are all related.
What is the frequency of light that has
wavelength of 100 nanometers?
What kind of electromagnetic radiation has a
wavelength of 100 meters?
15. * What is the wavelength of light that has a
frequency of 107.9 MHz (megahertz)?
16. * What is the energy of light that has a
wavelength of 0.00001 meters?
17. Name 2 uses for each form of light.
18. Compare and contrast the 3 types of spectra:
continuous, absorption, and emission.
19. How do scientists determine the elements that
make up a star?
20. Why do sailors at sea like to wear polarized
sunglasses on sunny days?
21. How do rainbows form in Earth's atmosphere?
22. How can you be sure that what you see is not an
illusion?
23. Describe how a spectroscope works.
24. Design a circular arrangement of flat mirrors that
allows a single beam of light to go around and
around forever. Draw the arrangement using a
protractor and show the angles of incidence and
reflection.
Related Web Sites
The following are some web sites that are related to this lesson. You are encouraged to check out these sites to obtain additional information.
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http://en.wikipedia.org/wiki/Electromagnetic_radiation
http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/2-what-is-electromagnetic-radiation.html
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
http://www.astronomynotes.com/light/s3.htm
http://en.wikipedia.org/wiki/Remote_sensing
http://landsat.gsfc.nasa.gov/education/tutorials.html
Related Book Pages
The following are the pages from your book that correspond to this lesson.
Comprehensive E.S. Book
pp. 484-485 and 674-677
Intensive/Honors E.S. Book
pp. 37-39 and 747-748
Meteorology/GIS Book
Massachusetts Standards
The following are the Massachusetts Framework Standards that correspond to this lesson.
Earth Science Learning Standard(s) 1.1, 1.2, and 1.8
What’s Next?
Notes
2
CCI.
ELECTROMAGNETIC RADIATION A. Electromagnetic radiation is another name for visible and invisible light 1. Light moves and behaves like an ocean wave and sometimes behaves like a particle that has no mass, called a photon a. wavelength – the distance between the crests of two adjacent waves b. frequency – number of waves that pass a given point each second c. As frequency of wave increases, wavelength decreases and vice versa d. Higher frequency light has higher energy than lower frequency light and is more dangerous to life e. Photons can exert a force, or push, on matter. This is called radiation pressure. 2. Light travels 300,000 kilometers per second (670,000,000 mi/h, 186,000 mi/s) in a vacuum like space a. Light slows down when it travels through materials like air and water that have a higher density than space i. When light slows down, its direction bends (refraction) ii. Shorter wavelengths bend more than longer wavelengths b. The speed of light is constant, meaning it does not change randomly; hence the symbol for light is c. B. The Electromagnetic Spectrum 1. electromagnetic spectrum – arrangement of all wavelengths of light from longest to shortest wavelengths a. radio waves – longest wavelengths, lowest frequencies; used for TV, radio, communication b. Microwaves – communication, cell phones, wi‐fi, radar, cooking c. Infrared (IR) waves – heat, remote controls d. Visible light i.
only form of light humans can see with eyes ii.
white light is actually all colors combined and can be broken into Roy G. Biv (red, orange, yellow, green, blue, indigo, violet) by a prism  red has longest wavelength of visible light  violet has shortest wavelength of visible light iii.
true blackness is the absence of all wavelengths of light e. Ultraviolet (UV) waves – tanning, skin cancer, blindness f. X‐rays (X radiation) – broken bones g. Gamma rays – shortest wavelengths, highest frequencies; nuclear decay, cancer treatment 2. A pneumonic device for remembering the order of light is Red Martians Invaded Venus Using X‐ray Guns. 3. All matter emits electromagnetic radiation. The hotter the matter, the shorter the wavelengths of the radiation. C. Spectroscopy 1. Spectroscopy is the study of the properties of light that relate to wavelength. Spectroscopy uses a prism or similar object to diffract light and break it apart to display the individual wavelengths that make up the light. 2. Spectroscopy can be used to identify materials, because the pattern of wavelengths that materials emit, absorb, or reflect is often a defining characteristic of the material 3. Spectra i. Continuous spectrum – produced by a hot, incandescent solid, liquid, or gas under high pressure (e.g. star) ii. Emission spectra – produced by a hot gas under low pressure; spectral lines indicate the type of gas iii. Absorption spectra– produced when visible light passes through a relatively cool gas under low pressure that absorbs certain wavelengths leaving black bands in the spectrograph This page was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version.
Properties of Light
Electric and magnetic fields oscillate together but perpendicular to each other and the electromagnetic wave moves in a direction
perpendicular to both of the fields.
Light, electricity, and magnetism are manifestations of the same thing called electromagnetic radiation. The
energy you see coming out of the computer screen you are using to read this page is made of fluctuating electric
and magnetic energy fields. The electric and magnetic fields oscillate at right angles to each other and the
combined wave moves in a direction perpendicular to both of the electric and magnetic field oscillations. This
energy also comes in many forms that are not detectable with our eyes such as infrared (IR), radio, X-rays,
ultraviolet (UV), and gamma rays.
We feel infrared light as heat and our radios pick up the messages encoded in radio waves emitted by radio
stations. Ultraviolet light has high enough energy to damage our skin cells, so our bodies will produce a darker
pigment in our skin to prevent exposure of the deeper skin cells to the UV (we tan as a defense mechanism). The
special bulbs called ``black lights'' produce a lot of UV and were used by hospitals to kill bacteria, amoebas, and
other micro-organisms. X-rays are produced by very hot things in space. X-rays have more energy than UV, so
they can pass through skin, muscles, and organs. They are blocked by bones, so when the doctor takes your Xray, the picture that results is the shadow image of the X-rays that passed through your body. Because X-rays
have such high energy, they can damage or kill cells. A few brief exposures to low-intensity X-rays is okay. The Xray technician would be exposed to thousands of X-ray exposures if s/he did not use some sort of shielding.
Gamma rays are the most energetic form of electromagnetic radiation and are produced in nuclear reactions.
This page was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version.
The form of electromagnetic radiation your eyes can detect is called ``visible'' or ``optical''. Astronomers have only
recently (within the past few decades) been able to use the other forms of electromagnetic radiation or light. Every
time technology has been developed to detect another form of light, a revolution in our understanding of the
universe has occurred. The figure above shows all of the forms of electromagnetic radiation in order of INcreasing
wavelength (given in nanometers (nm)) and DEcreasing energy. Notice how tiny the visible band is!
There are some general properties shared by all forms of electromagnetic radiation:
1. It can travel through empty space. Other types of waves need some sort of medium to move through:
water waves need liquid water and sound waves need some gas, liquid, or solid material to be heard.
2. The speed of light is constant in space. All forms of light have the same speed of 299,800
kilometers/second in space (often abbreviated as c). From highest energy to lowest energy the forms of
light are Gamma rays, X-rays, Ultraviolet, Visible, Infrared, Radio. (Microwaves are high-energy radio
waves.)
3. A wavelength of light is defined similarly to that of water waves---distance between crests or between
troughs. Visible light (what your eye detects) has wavelengths 4000-8000 Ångstroms. 1 Ångstrom = 10-10
meter. Visible light is sometimes also measured in nanometers (``nm'' in the figure above): 1 nanometer =
10-9 meter = 10 Ångstroms, so in nanometers, the visible band is from 400 to 800 nanometers. Radio
wavelengths are often measured in centimeters: 1 centimeter = 10-2 meter = 0.01 meter. The abbreviation
used for wavelength is the greek letter lambda: .
White light is made of different colors (wavelengths). When white light is passed through a prism or diffraction
grating, it is spread out into all of its different colors. You see this happen every time you see a rainbow. Not all
wavelengths of light from space make it to the surface. Only long-wave UV, Visible, parts of the IR and radio
bands make it to surface. More IR reaches elevations above 9,000 feet (2765 meters) elevation. That is one
reason why modern observatories are built on top of very high mountains. Fortunately, as far as life is concerned,
our atmosphere shields us from the gamma rays, X-rays, and most of the UV. It also blocks most of the IR and
parts of the radio. Astronomers were not able to detect these forms of energy from celestial objects until the
space age, when they could put satellite observatories in orbit.
Besides using wavelength to describe the form of light, you can also use the frequency--the number of crests of
the wave that pass by a point every second. Frequency is measured in units of hertz (Hz): 1 hertz = 1 wave
crest/second. For light there is a simple relation between the speed of light (c), wavelength ( ), and frequency (f):
f = c/ .
Since the wavelength is in the bottom of the fraction, the frequency is inversely proportional to the wavelength.
This means that light with a smaller wavelength has a higher (larger) frequency. Light with a longer wavelength
has a lower (smaller) frequency.
This page was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and corrected version.
The animation shows waves with different wavelengths moving to the right with the same speed. The bottom
wave has a wavelength = 3×(wavelength of the top wave). The counter shows how many wavelengths of the top
wave have passed the dashed line. In one second, the top wave moves three wavelengths to the right so its
frequency is 3 Hz. The bottom wave moves one of its wavelengths in one second so its frequency is 1 Hz (=
1/3×top wave frequency).
Some colors and their approximate wavelength, frequency and energy ranges are given in the table below. The
unit of energy is the Joule (J). A Joule is how much energy you expend when you lift an object with 1 kilogram of
mass (for example, a liter of water) about 10 centimeters above the ground. If you then let it go, the object hits the
ground with that much energy. Sometimes light energy is also measured in ``ergs'', where 1 erg = 10-7 Joule.
(Å)
color
f (*1014 Hz) Energy (*10-19 J)
violet 4000
4600 7.5
6.5
5.0
4.3
indigo 4600
4750 6.5
6.3
4.3
4.2
4750
4900 6.3
6.1
4.2
4.1
green 4900
5650 6.1
5.3
4.1
3.5
yellow 5650
5750 5.3
5.2
3.5
3.45
orange 5750
6000 5.2
5.0
3.45
3.3
8000 5.0
3.7
3.3
2.5
blue
red
6000
Note the trends: bluer light has shorter , higher f, and more energy. Redder light has longer , lower f, and less
energy.
Review Questions
1. Why is light so very important to astronomy? What kinds of information can you get from it?
2. Why is light called electromagnetic radiation? Is radio a form of light?
3. Put the following forms of light in order of increasing frequency (lowest frequency first): ultraviolet,
infrared, gamma rays, visible, radio, X-rays. Put them in order of increasing wavelength (shortest
wavelength first). Put them in order of increasing energy (lowest energy first).
4. Do all forms of light travel at the same speed in a vacuum (empty space)? Why is it important that light
can travel through empty space?
5. What forms of light can be observed from the ground (including high mountains)? What forms can be
observed at high altitudes in our atmosphere? What forms must be observed in space?
Examples:
Examples:
LOW
LOW
LONG
Microwaves
Radio
Waves
Examples:
Infrared
Radiation
(IR)
ENERGY
FREQUENCY
WAVELENGTH
Examples:
(ROY G. BIV)
Visible
Light
Examples:
Ultraviolet
Radiation
(UV)
THE ELECTROMAGNETIC SPECTRUM
Examples:
X-rays
HIGH
HIGH
SHORT
Examples:
Gamma
Rays
Physicists in
Texas have
developed a
method to make
objects
"invisible" within
a limited range of
light waves. It's
not Harry Potter's
invisibility cloak
just yet, but
scientists say it
has a lot of
potential.
(CNN) -- Some
scientists seem to
take their cues
from science
fiction or fantasy
novels.
CNN.com
Page 1 of 2
27/03/2013 06:20 AM
This is not the first time scientists have made an object 'invisible,' but previous methods have involved hulking devices and more
cumbersome methods.
The discovery could advance the fields of specialty optics and biotechnology, according to the physicists.
Scientists, on the other hand, find this development exciting because it could prove useful in nanotechnology by letting light bypass
microscopic objects that would otherwise block it.
Useful in nanotechnology
The effect only covers a very small band of electromagnetic waves at one time, and in the visible range of light, it would only work
on objects much thinner than a single strand of hair.
Doing so would then make objects invisible to the human eye.
New technology makes troops invisible
In their experiment, the physicists covered a cylinder about a foot long and an
inch or so in diameter with the material. Microwave detectors could no longer
plainly 'see' it, although it was still visible to the human eye. But the same principle could be transferred to the range of perceptible
light, researchers say.
The future is not here just yet
If an object is wrapped in it, it 'disappears,' but the effect only applies to a
limited range of light waves -- specifically microwaves.
Researchers at the University of Texas in Austin have developed a thin
material called a 'mantle cloak,' according to a report published in the New
Journal of Physics Tuesday.
A fixture in magic, the invisibility cloak has now advanced to science.
The desire to
become invisible dates back to the ancient Greeks, if not further. In mythological literature, gods and goddesses donned a headdress
to disappear from sight. Like Potter's cloak, the "cap of invisibility" was imbued with magical powers.
It doesn't look as cool as Harry Potter's invisibility cloak, but this is real science, not movie magic.
By Ben Brumfield , CNN
updated 7:45 AM EDT, Wed March 27, 2013 |
Scientists come a step closer to invisibility cloak
http://www.cnn.com/2013/03/27/tech/invisibility-cloak/index.html?iid=article_sidebar
Page 2 of 2
© 2013 Cable News Network. Turner Broadcasting System, Inc. All Rights Reserved.
Perhaps the cloak would make a good ingredient in car paint.
Microwaves, which the mantle cloak currently does neutralize, are used in radar detectors.
27/03/2013 06:20 AM
Although the scientists say the principle behind the cloak could currently only be used to hide objects from the human eye that are so
tiny it can't see them anyhow, they say it could "pave the way" to the development of advanced "camouflaging and invisibility."
It has no effect on a vast array of electromagnetic waves, which come in a myriad of sizes. The light waves we can see make up only
a thin sliver of them.
For it to work, the material's pattern has to be roughly the size of the wavelength of light to be canceled out. That gives it a tightly
limited range of waves it will work on.
It is made by combining copper tape with polycarbonate, a material commonly used in DVD's and CDs. The resulting cloak has a
miniscule pattern -- like a finely checkered shirt -- that neutralizes the waves bouncing off of it.
The cloak's material
Light is a wave that can be disturbed. That's what the mantle cloak does.
The mantle cloak takes a new approach.
Previous attempts at achieving invisibility have involved bending or reflecting light around the object that is meant to vanish.
Light also refracts -- or breaks -- when it passes through a prism or raindrops, resulting in the palette of colors we see in a rainbow. It
also bends ever so slightly due to gravity, when it passes by a planet.
Light has properties that can be manipulated, which is how objects can be rendered invisible. It can be reflected away, for example.
Illusionists such as David Copperfield can use mirrors to make an object disappear.
We see things because light reflects off of them and hits our eyes. Or, in this case, microwaves bounce off of them and hit a detection
device.
Light and invisibility
http://www.cnn.com/2013/03/27/tech/invisibility-cloak/index.html?iid=article_sidebar
The new cloak is made of a sheer, handy material that can be applied to many surfaces, even irregular ones, according to the report.
http://www.cnn.com/2013/09/26/us/new-lightsaber-molecule/index.html?hpt=hp_t3
Scientists create light-matter like Darth Vader's lightsaber
By Ben Brumfield , CNN
updated 9:49 AM EDT, Thu September 26, 2013
CNN.com
(CNN) -- A beam of light is supposed to shine off into
infinity, but when Darth Vader and Luke Skywalker whip
out their lightsabers for some spark-flying action, the
light blades extrude like stick deodorant and then just
stop.
It's like they're sticks of light-matter.
Hollywood may have made that stuff up, but now,
scientists at MIT and Harvard have actually made that
stuff -- not enough for a lightsaber, only a subatomic
smidgeon. But even that much is a big deal.
Darth Vader wields a lightsaber. Scientists have created molecules that behave a bit like the matter in the
fictional weapons.
Light-matter existed previously only in theory, but now,
for the first time, it has been observed in reality,
researchers from the Center for Ultracold Atoms say.
To oversimplify things, we'll say that photons are subatomic particles that make up light. They have no detectable mass the way most matter
does, and usually, they don't stick together. You can shoot two lasers at each other, and the photons will pass right through one another.
But physicists Mikhail Lukin and Vladan Vuletic recently got them to stick together to form molecules.
They published the results of their work in the science journal Nature this week
The newly created photon molecules don't behave like traditional light, but more like a lightsaber, Lukin said. "The physics of what's
happening in these molecules is similar to what we see in the movies."
But don't picture yourself swashbuckling with a lightsaber just yet. As in the creation of pretty much all unusual matter, scientists have to
produce extreme conditions in laboratories that can't exist naturally anywhere on Earth.
They pumped atoms of rubidium, a kind of metal, into a vacuum chamber -- air would otherwise rapidly alter them. This created a metal cloud
that they cooled down with lasers to about -450 degrees Fahrenheit, near what is called absolute zero. That makes atoms almost stand still.
Then they the fired photons into the atom cloud.
The photons, elements of light, did not shoot through at the speed of light but acted a little like regular matter instead. They bumped into the
atoms in a way similar to the way regular matter would.
In the process, the photons slowed down enough to bump into each other and bond into molecules.
It was a first.
Though that's fascinating, it doesn't make for a handy lightsaber.
But it could help in the future development of super computers known as quantum computers, Lukin said. And with some work, scientists
could make whole crystals out of light.
So, if Darth Vader shows up with a lightsaber, your great-grandchildren may be able to throw photon rocks at him.
But don't count on it.
© 2013 Cable News Network. Turner Broadcasting System, Inc. All Rights Reserved.
Page 1 of 1
Sep 26, 2013 11:44:31AM MDT
EARTH SCIENCE
Overall Score:
Light Review
Overall Grade:
Name______________________
Group______________________
5 Points
Date______________________
PART A (9 points)
Answer the following questions.
List all of the forms of light in
order of decreasing energy,
beginning with the highest
energy.
List all of the forms of light in
order of increasing frequency,
beginning with the lowest
frequency.
List all of the forms of light,
including colors of visible light, in
order of increasing wavelength,
beginning with the longest
wavelength.
1.
1.
1.
2.
2.
2.
3.
3.
3.
4.
4.
4.
5.
5.
5.
6.
6.
6.
7.
7.
7.
8.
9.
10.
11.
12.
13.
PART B (1 point)
What is the name given to “all forms of light”? _____________________________
Page 1 of 1