Electromagnetic Radiation
Jean Brainard, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2014 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: November 13, 2014
AUTHOR
Jean Brainard, Ph.D.
EDITOR
Bradley Hughes, Ph.D.
www.ck12.org
Chapter 1. Electromagnetic Radiation
C HAPTER
1
Electromagnetic Radiation
C HAPTER O UTLINE
1.1
Electromagnetic Waves
1.2
Properties of Electromagnetic Waves
1.3
The Electromagnetic Spectrum
1.4
References
Why is this picture of a cat so colorful? No cat looks like this to the human eye. The picture was taken with a special
camera that senses infrared light. This is a form of energy given off by warm objects. Areas that appear yellow are
the warmest, and areas that appear purple are the coolest. The picture shows that the cat’s eyes are the warmest part
of its head. Why can’t people see images like this without a camera? The answer has to do with the wavelengths of
infrared light. Its wavelengths are too long for the human eye to detect. In fact, the human eye can detect light only
in a very narrow range of wavelengths, called visible light. You’ll learn more about infrared light, visible light, and
other forms of electromagnetic radiation in this chapter.
Flickr:yellowcloud. www. f lickr.com/photos/yellowcloud/6375882963/. CC BY 2.0.
1
1.1. Electromagnetic Waves
www.ck12.org
1.1 Electromagnetic Waves
Lesson Objectives
•
•
•
•
•
Describe electromagnetic waves.
Explain how electromagnetic waves begin.
State how electromagnetic waves travel.
Summarize the wave-particle theory of light.
Identify sources of electromagnetic waves.
Lesson Vocabulary
• electromagnetic radiation
• electromagnetic wave
• photon
Introduction
Both infrared light and visible light are examples of electromagnetic radiation. Electromagnetic radiation is the
transfer of energy by waves traveling through matter or across empty space. The waves that transfer this energy are
called electromagnetic waves. In this lesson, you’ll learn how electromagnetic waves differ from mechanical waves
such as ocean waves and sound waves. For an excellent video introduction to electromagnetic waves, go to this
URL: http://www.youtube.com/watch?v=cfXzwh3KadE (5:20).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5046
What Are Electromagnetic Waves?
An electromagnetic wave is a wave that consists of vibrating electric and magnetic fields. A familiar example will
help you understand the fields that make up an electromagnetic wave. Think about a common bar magnet. It exerts
magnetic force in an area surrounding it, called the magnetic field. You can see the magnetic field of a bar magnet in
Figure 1.1. Because of this force field, a magnet can exert force on objects without touching them. They just have
to be in its magnetic field. An electric field is similar to a magnetic field (see Figure 1.1). An electric field is an area
2
www.ck12.org
Chapter 1. Electromagnetic Radiation
of electrical force surrounding a charged particle. Like a magnetic field, an electric field can exert force on objects
over a distance without actually touching them.
FIGURE 1.1
Magnetic and electric fields are invisible areas of force surrounding magnets and charged particles. The field
lines in the diagrams represent the direction and location of the force.
How Electromagnetic Waves Begin
An electromagnetic wave begins when an electrically charged particle vibrates. This is illustrated in Figure 1.2.
When a charged particle vibrates, it causes the electric field surrounding it to vibrate as well. A vibrating electric
field, in turn, creates a vibrating magnetic field (you can learn how this happens in the chapter "Electromagnetism").
The two types of vibrating fields combine to create an electromagnetic wave. You can see an animation of an
electromagnetic wave at this URL: http://www.youtube.com/watch?v=Qju7QnbrOhM (1:31).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5047
3
1.1. Electromagnetic Waves
www.ck12.org
FIGURE 1.2
An electromagnetic wave starts with a
vibrating charged particle.
How Electromagnetic Waves Travel
As you can see in Figure 1.2, the electric and magnetic fields that make up an electromagnetic wave occur are at
right angles to each other. Both fields are also at right angles to the direction that the wave travels. Therefore, an
electromagnetic wave is a transverse wave.
No Medium Required
Unlike a mechanical transverse wave, which requires a medium, an electromagnetic transverse wave can travel
through space without a medium. Waves traveling through a medium lose some energy to the medium. However,
when an electromagnetic wave travels through space, no energy is lost, so the wave doesn’t get weaker as it travels.
However, the energy is "diluted" as it spreads out over an ever-larger area as it travels away from the source. This is
similar to the way a sound wave spreads out and becomes less intense farther from the sound source.
Wave Interactions
Electromagnetic waves can travel through matter as well as across space. When they strike matter, they interact with
it in the same ways that mechanical waves interact with matter. They may reflect (bounce back), refract (bend when
traveling through different materials), or diffract (bend around objects). They may also be converted to other forms
of energy. Microwaves are a familiar example. They are a type of electromagnetic wave that you can read about
later on in this chapter, in the lesson "The Electromagnetic Spectrum." When microwaves strike food in a microwave
oven, they are converted to thermal energy, which heats the food.
Wave or Particle?
Electromagnetic radiation behaves like waves of energy most of the time, but sometimes it behaves like particles.
As evidence accumulated for this dual nature of electromagnetic radiation, the famous physicist Albert Einstein
4
www.ck12.org
Chapter 1. Electromagnetic Radiation
developed a new theory about electromagnetic radiation, called the wave-particle theory. This theory explains how
electromagnetic radiation can behave as both a wave and a particle. In brief, when an electron returns to a lower
energy level, it is thought to give off a tiny "packet" of energy called a photon (see Figure 1.3). The amount of
energy in a photon may vary. It depends on the frequency of electromagnetic radiation. The higher the frequency is,
the more energy a photon has.
FIGURE 1.3
A photon of light energy is given off when
an electron returns to a lower energy
level.
Sources of Electromagnetic Radiation
The most important source of electromagnetic radiation on Earth is the sun. Electromagnetic waves travel from the
sun to Earth across space and provide virtually all the energy that supports life on our planet. Many other sources of
electromagnetic waves that people use depend on technology. Radio waves, microwaves, and X rays are examples.
We use these electromagnetic waves for communications, cooking, medicine, and many other purposes. You’ll learn
about all these types of electromagnetic waves in this chapter’s lesson on "The Electromagnetic Spectrum."
Lesson Summary
• An electromagnetic wave consists of vibrating electric and magnetic fields.
• An electromagnetic wave begins when an electrically charged particle vibrates.
• Electromagnetic waves are transverse waves that can travel across space without a medium. When the waves
strike matter, they may reflect, refract, or diffract, or they may be converted to other forms of energy.
• Electromagnetic radiation behaves like particles as well as waves. This prompted Albert Einstein to develop
his wave-particle theory.
• The most important source of electromagnetic waves on Earth is the sun, which provides virtually all the
energy that supports life on Earth. Other sources of electromagnetic radiation depend on technology and are
used for communications, cooking, and other purposes.
5
1.1. Electromagnetic Waves
www.ck12.org
Lesson Review Questions
Recall
1.
2.
3.
4.
5.
Define electromagnetic radiation.
What is an electromagnetic wave?
How do electromagnetic waves interact with matter?
What is a photon?
Identify sources of electromagnetic waves.
Apply Concepts
6. Create a diagram to represent an electromagnetic wave. Explain your diagram to another student who has no
prior knowledge of electromagnetic waves.
Think Critically
7. Explain how an electromagnetic wave begins.
8. Compare and contrast mechanical transverse waves and electromagnetic transverse waves.
Points to Consider
In this lesson, you learned that electromagnetic waves are transverse waves. Like other transverse waves, electromagnetic waves have certain properties.
• Based on your knowledge of other transverse waves, such as waves in a rope, what is the wavelength of an
electromagnetic wave? How is it measured?
• How do you think the wavelengths of electromagnetic waves are related to their frequencies? (Hint: How is
the speed of waves calculated?)
6
www.ck12.org
Chapter 1. Electromagnetic Radiation
1.2 Properties of Electromagnetic Waves
Lesson Objectives
• Describe the speed of electromagnetic waves.
• Relate wavelength and frequency of electromagnetic waves.
Lesson Vocabulary
• speed of light
Introduction
Some electromagnetic waves are harmless. The light we use to see is a good example. Other electromagnetic waves
are very harmful. They can penetrate virtually anything and destroy living cells. Why do electromagnetic waves
vary in these ways? It depends on their properties. Like other waves, electromagnetic waves have properties of
speed, wavelength, and frequency.
Speed of Electromagnetic Waves
All electromagnetic waves travel at the same speed through empty space. That speed, called the speed of light, is
300 million meters per second (3.0 × 108 m/s). Nothing else in the universe is known to travel this fast. If you could
move that fast, you would be able to travel around Earth 7.5 times in just 1 second! The sun is about 150 million
kilometers (93 million miles) from Earth, but it takes electromagnetic radiation only 8 minutes to reach Earth from
the sun. Electromagnetic waves travel more slowly through a medium, and their speed may vary from one medium
to another. For example, light travels more slowly through water than it does through air (see Figure 1.4). You can
learn more about the speed of light at this URL: http://videos.howstuffworks.com/discovery/29407-assignment-d
iscovery-speed-of-light-video.htm .
FIGURE 1.4
Light slows down when it enters water from the air. This causes the wave
to refract, or bend.
7
1.2. Properties of Electromagnetic Waves
www.ck12.org
Wavelength and Frequency of Electromagnetic Waves
Although all electromagnetic waves travel at the same speed, they may differ in their wavelength and frequency.
Defining Wavelength and Frequency
Wavelength and frequency are defined in the same way for electromagnetic waves as they are for mechanical waves.
Both properties are illustrated in Figure 1.5.
• Wavelength is the distance between corresponding points of adjacent waves. Wavelengths of electromagnetic
waves range from many kilometers to a tiny fraction of a millimeter.
• Frequency is the number of waves that pass a fixed point in a given amount of time. Frequencies of electromagnetic waves range from thousands to trillions of waves per second. Higher frequency waves have greater
energy.
FIGURE 1.5
Wavelength and frequency of electromagnetic waves.
Speed, Wavelength, and Frequency
The speed of a wave is a product of its wavelength and frequency. Because all electromagnetic waves travel at the
same speed through space, a wave with a shorter wavelength must have a higher frequency, and vice versa. This
relationship is represented by the equation:
Speed = Wavelength × Frequency
The equation for wave speed can be rewritten as:
Frequency =
8
Speed
Speed
or Wavelength =
Wavelength
Frequency
www.ck12.org
Chapter 1. Electromagnetic Radiation
Therefore, if either wavelength or frequency is known, the missing value can be calculated. Consider an electromagnetic wave that has a wavelength of 3 meters. Its speed, like the speed of all electromagnetic waves, is 3.0 × 108
meters per second. Its frequency can be found by substituting these values into the frequency equation:
Frequency =
3.0 × 108 m/s
= 1.0 × 108 waves/s, or 1.0 × 108 hertz (Hz)
3.0 m
You Try It!
Problem: What is the wavelength of an electromagnetic wave that has a frequency of 3.0 × 108 hertz?
For more practice calculating the frequency and wavelength of electromagnetic waves, go to these URLs:
• http://www.youtube.com/watch?v=GwZvtfZRNKk
• http://www.youtube.com/watch?v=wjPk108Ua8k
Lesson Summary
• All electromagnetic waves travel at the same speed through space, called the speed of light, which equals 3.0
× 108 meters per second. Electromagnetic waves travel more slowly through a medium.
• Electromagnetic waves differ in their wavelengths and frequencies. The higher the frequency of an electromagnetic wave, the greater its energy. The speed of an electromagnetic wave is the product of its wavelength
and frequency, so a wave with a shorter wavelength has a higher frequency, and vice versa.
Lesson Review Questions
Recall
1. What is the speed of light?
2. What is the wavelength of an electromagnetic wave?
3. Describe the range of frequencies of electromagnetic waves.
Apply Concepts
4. If an electromagnetic wave has a wavelength of 1 meter, what is its frequency?
Think Critically
5. Explain why light waves bend when they pass from air to water at an angle.
6. Explain the relationship between frequency and wavelength of electromagnetic waves.
Points to Consider
In this lesson, you learned that electromagnetic waves vary in their wavelength and frequency. The complete range
of wavelengths and frequencies of electromagnetic waves is outlined in the next lesson, "The Electromagnetic
9
1.2. Properties of Electromagnetic Waves
Spectrum."
• What do you think are the longest-wavelength electromagnetic wave?
• What might be the electromagnetic waves with the highest frequencies?
10
www.ck12.org
www.ck12.org
Chapter 1. Electromagnetic Radiation
1.3 The Electromagnetic Spectrum
Lesson Objectives
•
•
•
•
Define the electromagnetic spectrum.
Describe radio waves and their uses.
Identify three forms of light.
Describe X rays and gamma rays.
Lesson Vocabulary
•
•
•
•
•
•
•
•
•
electromagnetic spectrum
gamma ray
infrared light
microwave
radar
radio wave
ultraviolet light
visible light
X ray
Introduction
Imagine playing beach volleyball, like the young men in Figure 1.6. They may not realize it, but they are being
bombarded by electromagnetic radiation as play in the sunlight. The only kinds of radiation they can detect are
visible light, which allows them to see, and infrared light, which they feel as warmth on their skin. What other kinds
of electromagnetic radiation are they being exposed to in sunlight? In this lesson, you’ll find out.
What Is The Electromagnetic Spectrum?
Electromagnetic radiation occurs in waves of different wavelengths and frequencies. Infrared light and visible
light make up just a small part of the full range of electromagnetic radiation, which is called the electromagnetic
spectrum. The electromagnetic spectrum is summarized in the diagram in Figure 1.7.
• On the far left of the diagram are radio waves, which include microwaves. They have the longest wavelengths
and lowest frequencies of all electromagnetic waves. They also have the least amount of energy.
• On the far right are X rays and gamma rays. The have the shortest wavelengths and highest frequencies of all
electromagnetic waves. They also have the greatest amount of energy.
11
1.3. The Electromagnetic Spectrum
www.ck12.org
FIGURE 1.6
Electromagnetic radiation from the sun
reaches Earth across space.
It strikes
everything on Earth’s surface, including
these volleyball players.
• Between these two extremes, wavelength, frequency, and energy change continuously from one side of the
spectrum to the other. Waves in this middle section of the electromagnetic spectrum are commonly called
light.
As you will read below, the properties of electromagnetic waves influence how the different waves behave and how
they can be used.
FIGURE 1.7
How do the wavelength and frequency of waves change across the electromagnetic spectrum?
12
www.ck12.org
Chapter 1. Electromagnetic Radiation
Radio Waves
Radio waves are the broad range of electromagnetic waves with the longest wavelengths and lowest frequencies.
In Figure 1.7, you can see that the wavelength of radio waves may be longer than a soccer field. With their low
frequencies, radio waves have the least energy of electromagnetic waves, but they still are extremely useful. They
are used for radio and television broadcasts, microwave ovens, cell phone transmissions, and radar. You can learn
more about radio waves, including how they were discovered, at this URL: http://www.youtube.com/watch?v=al7sF
P4C2TY (3:58).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5048
AM and FM Radio
In radio broadcasts, sounds are encoded in radio waves that are sent out through the atmosphere from a radio tower.
A receiver detects the radio waves and changes them back to sounds. You’ve probably listened to both AM and FM
radio stations. How sounds are encoded in radio waves differs between AM and FM broadcasts.
• AM stands for amplitude modulation. In AM broadcasts, sound signals are encoded by changing the amplitude
of radio waves. AM broadcasts use longer–wavelength radio waves than FM broadcasts. Because of their
longer wavelengths, AM radio waves reflect off a layer of the upper atmosphere called the ionosphere. You
can see how this happens in Figure 1.8. This allows AM radio waves to reach radio receivers that are very far
away from the radio tower.
• FM stands for frequency modulation. In FM broadcasts, sound signals are encoded by changing the frequency
of radio waves. Frequency modulation allows FM waves to encode more information than does amplitude
modulation, so FM broadcasts usually sound clearer than AM broadcasts. However, because of their shorter
wavelength, FM waves do not reflect off the ionosphere. Instead, they pass right through it and out into space
(see Figure 1.8). As a result, FM waves cannot reach very distant receivers.
FIGURE 1.8
AM radio waves reflect off the ionosphere
and travel back to Earth. Radio waves
used for FM radio and television pass
through the ionosphere and do not reflect
back.
13
1.3. The Electromagnetic Spectrum
www.ck12.org
Television
Television broadcasts also use radio waves. Sounds are encoded with frequency modulation, and pictures are
encoded with amplitude modulation. The encoded radio waves are broadcast from a TV tower like the one in
Figure 1.9. When the waves are received by television sets, they are decoded and changed back to sounds and
pictures.
FIGURE 1.9
This television tower broadcasts signals
using radio waves.
Microwaves
The shortest wavelength, highest frequency radio waves are called microwaves (see Figure 1.7). Microwaves have
more energy than other radio waves. That’s why they are useful for heating food in microwave ovens. Microwaves
have other important uses as well, including cell phone transmissions and radar, which is a device for determining
the presence and location of an object by measuring the time for the echo of a radio wave to return from it and the
direction from which it returns. These uses are described in Figure 1.10. You can learn more about microwaves and
their uses in the video at this URL: http://www.youtube.com/watch?v=YgQQb1BVnu8 (3:23).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5049
Light
Mid-wavelength electromagnetic waves are commonly called light. This range of electromagnetic waves has shorter
wavelengths and higher frequencies than radio waves, but not as short and high as X rays and gamma rays. Light
includes visible light, infrared light, and ultraviolet light. If you look back at Figure 1.7, you can see where these
different types of light waves fall in the electromagnetic spectrum.
Visible Light
The only light that people can see is called visible light. It refers to a very narrow range of wavelengths in the
electromagnetic spectrum that falls between infrared light and ultraviolet light. Within the visible range, we see light
14
www.ck12.org
Chapter 1. Electromagnetic Radiation
FIGURE 1.10
Microwaves are used for cell phones and radar.
of different wavelengths as different colors of light, from red light, which has the longest wavelength, to violet light,
which has the shortest wavelength. You can see the spectrum of colors of visible light in Figure 1.11. When all of
the wavelengths are combined, as they are in sunlight, visible light appears white. You can learn more about visible
light in the chapter "Visible Light" and at the URL below.
15
1.3. The Electromagnetic Spectrum
www.ck12.org
http://www.youtube.com/watch?v=PMtC34pzKGc (4:50)
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5050
FIGURE 1.11
Red light (right) has the longest wavelength, and violet light (left) has the shortest wavelength.
Infrared Light
Light with the longest wavelengths is called infrared light. The term infrared means "below red." Infrared light is
the range of light waves that have longer wavelengths than red light in the visible spectrum. You can’t see infrared
light waves, but you can feel them as heat on your skin. The sun gives off infrared light as do fires and living
things. The picture of a cat that opened this chapter was made with a camera that detects infrared light waves and
changes their energy to colored light in the visible range. Night vision goggles, which are used by law enforcement
and the military, also detect infrared light waves. The goggles convert the invisible waves to visible images. For a
deeper understanding of infrared light, watch the video at this URL: http://www.youtube.com/watch?v=2–0q0XlQ
J0 (6:46).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5051
Ultraviolet Light
Light with wavelengths shorter than visible light is called ultraviolet light. The term ultraviolet means "above
violet." Ultraviolet light is the range of light waves that have shorter wavelengths than violet light in the visible
spectrum. Humans can’t see ultraviolet light, but it is very useful nonetheless. It has higher-frequency waves than
visible light, so it has more energy. It can be used to kill bacteria in food and to sterilize laboratory equipment (see
Figure 1.12). The human skin also makes vitamin D when it is exposed to ultraviolet light. Vitamin D is needed for
strong bones and teeth. You can learn more about ultraviolet light and its discovery at this URL: http://www.youtu
be.com/watch?v=QW5zeVy8aE0 (3:40).
16
www.ck12.org
Chapter 1. Electromagnetic Radiation
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/1587
FIGURE 1.12
This sterilizer for laboratory equipment
uses ultraviolet light to kill bacteria.
Too much exposure to ultraviolet light can cause sunburn and skin cancer. You can protect your skin from ultraviolet
light by wearing clothing that covers your skin and by applying sunscreen to any exposed areas. The SPF, or sunprotection factor, of sunscreen gives a rough idea of how long it protects the skin from sunburn (see Figure 1.13).
A sunscreen with a higher SPF protects the skin longer. You should use sunscreen with an SPF of at least 15 even
on cloudy days, because ultraviolet light can travel through clouds. Sunscreen should be applied liberally and often.
You can learn more about the effects of ultraviolet light on the skin at this URL: http://www.youtube.com/watch
?v=np-BBJyl-go (5:59).
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5052
X Rays and Gamma Rays
The shortest-wavelength, highest-frequency electromagnetic waves are X rays and gamma rays. These rays have
so much energy that they can pass through many materials. This makes them potentially very harmful, but it also
makes them useful for certain purposes.
17
1.3. The Electromagnetic Spectrum
www.ck12.org
FIGURE 1.13
If your skin normally burns in 10 minutes of sun exposure, using sunscreen
with an SPF of 30 means that, ideally, your skin will burn only after 30
times 10 minutes, or 300 minutes, of sun exposure. How long does
sunscreen with an SPF of 50 protect skin from sunburn?
X Rays
X rays are high-energy electromagnetic waves. They have enough energy to pass through soft tissues such as skin
but not enough to pass through bones and teeth, which are very dense. The bright areas on the X ray film in Figure
1.14 show where X rays were absorbed by the teeth. X rays are used not only for dental and medical purposes but
also to screen luggage at airports (see Figure 1.14). Too much X ray exposure may cause cancer. If you’ve had
dental X rays, you may have noticed that a heavy apron was placed over your body to protect it from stray X rays.
The apron is made of lead, which X rays cannot pass through. You can learn about the discovery of X rays as well
as other uses of X rays at this URL: http://www.guardian.co.uk/science/blog/2010/oct/26/x-ray-visions-disease-for
geries .
FIGURE 1.14
Two common uses of X rays are illustrated
here.
Gamma Rays
Gamma rays are the most energetic of all electromagnetic waves. They can pass through most materials, including
bones and teeth. Nonetheless, even these waves are useful. For example, they can be used to treat cancer. A medical
device sends gamma rays the site of the cancer, and the rays destroy the cancerous cells. If you want to learn more
about gamma rays, watch the video at the URL below.
http://www.youtube.com/watch?v=okyynBaSOtA (2:45)
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/5015
18
www.ck12.org
Chapter 1. Electromagnetic Radiation
KQED: Seeing Cells in 3-D
Scientists in Berkeley have developed a powerful new microscope which uses X rays to scan a whole cell and in a
manner of minutes, generate a 3D view of the cell and its genetic material. This groundbreaking tool is helping to
advance research into the development of biofuels, the treatment of malaria and it may even help to more rapidly
diagnose cancer. For more information on X ray microscopes, see http://science.kqed.org/quest/video/x-ray-micros
cope-seeing-cells-in-3-d/ .
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/129635
Lesson Summary
• The electromagnetic spectrum is the full range of wavelengths and frequencies of electromagnetic radiation.
Wavelength, frequency, and energy change continuously across the electromagnetic spectrum.
• Radio waves are the broad range of electromagnetic waves with the longest wavelengths and lowest frequencies. They are used for radio and television broadcasts, microwave ovens, cell phone transmissions, and radar.
• Mid-wavelength electromagnetic waves are called light. Light consists of visible, infrared, and ultraviolet
light. Humans can see only visible light. Infrared light has longer wavelengths than visible light and is
perceived as warmth. Ultraviolet light has shorter wavelengths than visible light and has enough energy to kill
bacteria. It can also harm the skin.
• X rays and gamma rays are the electromagnetic waves with the shortest wavelengths and highest frequencies.
X rays are used in medicine and dentistry and to screen luggage at airports. Gamma rays are used to kill cancer
cells.
Lesson Review Questions
Recall
1.
2.
3.
4.
What is the electromagnetic spectrum?
Describe how wave frequency changes across the electromagnetic spectrum, from radio waves to gamma rays.
List three uses of radio waves.
How are X rays and gamma rays used in medicine?
Apply Concepts
5. Create a public service video warming people of the dangers of ultraviolet light. Include tips for protecting
the skin from ultraviolet light.
19
1.3. The Electromagnetic Spectrum
www.ck12.org
Think Critically
6. Explain two ways that sounds can be encoded in electromagnetic waves.
7. Explain how radar works.
8. Compare and contrast infrared, visible, and ultraviolet light.
Points to Consider
This chapter introduces visible light. The chapter "Visible Light" discusses visible light in greater detail.
• In this lesson, you read that visible light consists of light of different colors. Do you know how visible light
can be separated into its different colors? (Hint: How does a rainbow form?)
• In the next chapter, Visible Light, you’ll read that visible light interacts with matter in certain characteristic
ways. Based on your own experiences with visible light, how does it interact with matter? (Hint: What
happens to visible light when it strikes a wall, window, or mirror?)
20
www.ck12.org
Chapter 1. Electromagnetic Radiation
1.4 References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
Alicia Bruce. http://www.flickr.com/photos/aliciaabruce/6883325921/ . CC BY 2.0
Courtesy of NASA. http://commons.wikimedia.org/wiki/File:EM_Spectrum3-new.jpg . Public Domain
Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
KaMa Photography. http://www.flickr.com/photos/katharina_90/3858883369/ . CC BY 2.0
Christopher Auyeung and Laura Guerin. CK-12 Foundation . CC BY-NC 3.0
User:Phrood/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Spectrum-sRGB.svg . Public
Domain
12. User:Newbie/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:UV-ontsmetting_laminaire-vloe
ikast.JPG . Public Domain
13. Tom Newby. http://www.flickr.com/photos/noodle93/5392321454/ . CC BY 2.0
14. Dental X ray: Paulo Ordoveza (Flickr:brownpau); Airport X ray: Gwydion M. Williams. Dental X ray:
http://www.flickr.com/photos/brownpau/4879544448/; Airport X ray: http://www.flickr.com/photos/4590911
1@N00/3766521804/ . CC BY 2.0
21