home work for science

CA Rev. 5/26/20201
General Science 1B
Credit 5
Rev. 5/5/21
NAME:_________________________
CREDIT 5B: WAVE PROPERTIES AND
ELECTROMAGNETIC RADIATION
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Lesson
Title
INTRODUCTION
5.1
Properties of Waves and Wave
Interactions
5.2
Electromagnetic Waves
5.3
Electromagnetic Radiation
Assignments

 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Simulating Wave Interference
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Electromagnetic Spectrum Concept Map
 Review Questions
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Roof Color and Temperature
 Constructed Response


PERFORMANCE TASK
QUIZ
Title
Icon
Student Support Icons
Description
Review
Activity
This provides the students with a reminder that they need to answer questions.
Technology
Guides students through the tasks and assignments that require the use of
technology and manipulatives.
Reading
This icon lets the students know they will be completing a reading activity.
Credit Materials
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Materials
Pen/Pencil
HMH Physics Textbook
(optional)
Packet
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Technology Needs
Internet
Computer
HMH Online Resources
(optional)
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NAME:_________________________
CREDIT 5B: INTRODUCTION
Read “What is a Wave?” and watch the video “What Does Sound Look Like?” below. Then answer the
essential question.
What is a Wave?
A wave is a disturbance that travels through space and transports energy. Electromagnetic waves (light) can
travel through a vacuum. Other waves, known as mechanical waves, can only travel through a medium such as
a solid, liquid, or gas.
You encounter waves daily. For example, you can see visible light waves and hear because of sound waves.
Waves exist in many forms; for instance, ripples on a pond or waves at a beach are waves that move through
water and earthquakes create waves that move through the ground. You may have seen people simulate a wave.
When a crowd does the “wave” at a sports event, they stand up and sit down in an organized way so that a ripple
effect travels person by person through the entire crowd.
The disturbance caused by waves is only temporary. Although a wave may transport energy from one place to
another, it does not transport mass. For example, during the crowd “wave” each person changes position, from
sitting to standing, for just a moment as the wave passes by. The people do not travel around the stadium with
the wave.
Adapted from “ASPIRE Lab | What Is a Wave?” PBS LearningMedia, PBS, www.pbslearningmedia.org/resource/lsps07.sci.phys.energy.waves/what-is-a-wave.
An essential question is something that allows you to explore what the credit is about. Before you answer the
question, examine the diagram below. Watch the video if you feel you need more information. Then, answer the
essential question to the best of your ability. You will revisit it at the end of the credit to see if your answer has
evolved.
Video: What Does Sound Look Like? (2:31)

“What Does Sound Look Like?” YouTube. NPR, 9 Apr. 213. Web.
Essential Question
How do invisible things such as sound and Wi-Fi internet travel from place to place?
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Credit 5
LESSON 5.1: PROPERTIES OF WAVES AND WAVE
INTERACTIONS
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Learning Goals for this Lesson
 Describe characteristics of wave behavior.
 Identify sources and causes of waves.
 Explain amplitude, frequency, and wavelength.
 Predict what will happen to waves when they interact with one another.
Lesson Assignments
 Connect to Essential Question
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Simulating Wave Interference
 Review Questions
Engage
Connect to Essential Question
Why are the ocean’s movements along the shore called waves? What do ocean waves have in common with
sound and light?
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Explore
Exploration Activity
Wave behavior is not limited to water, light, and sound; it can also be observed through objects. When you
wiggle a thread or garden hose, a wave starts at your hand and moves through the object. In this computer
simulation, you will observe how a wave passes through a string.
Procedure:
1. Open the PhET simulation: “Wave on a String”
https://phet.colorado.edu/en/simulation/wave-on-a-string
2. In the upper left, set the mode to “oscillate”. This will give you a constant, smooth wave.
3. In the upper right, set the simulation to “no end”. This will eliminate interference as the wave bounces
back.
4. On the bottom, change the speed to “slow motion” to make the wave easier to observe.
Analysis:
Use the simulation to answer the questions below.
1. In your own words, how would you describe the movement of the string?
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2. Focus on one of the green circles. Describe the movement of the green circles as the string moves.
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3. Change set the mode to “pulse” which is in the upper left corner. Change the option to “fixed end”
which is in the upper right corner. Reduce the damping slider to none (zero). Press the large green button
to pulse the wave, wait 2-3 seconds and pulse again, making a second wave. What happens to the first
wave when it reaches the fixed end?
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4. Describe the behavior of the string when the two waves run into each other.
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Paul, Ariel, Micahel Dubson, Jonathan Olson, Patricia Loeblein, Kathy Perkins, Amy Rouinfar, and Sharon Siman-Tov. “Wave on a String.” PhET. University of
Colorado Boulder, 2014. Web. 23 Feb. 2016. .
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What is a Wave?
Most of the information that we receive comes to us in the form of waves. Sound, light, radio, television, and
Internet travel via waves. When energy is transferred by a wave to a receiver, there is no transfer of matter
between the two points. This was observed during the “Wave on a String” simulation activity. The green dots
move up and down, but do not travel with the wave. It is energy within the string that is moving, rather than the
string itself.
When you throw a stone into a pond, a wave is produced that expands out in a circle. It is the energy from the
disturbance that is moving, not the water itself. Once the disturbance has passed, the water is where it was
before the disturbance occurred. When someone shouts your name from across a room, the sound wave is a
disturbance in the air that travels across the room. The air molecules do not move; the air is only the medium
through which energy travels. A medium is a physical environment in which a disturbance can travel. A wave
is a disturbance within a medium. The energy transferred from a source to a receiver is carried by a disturbance
in a medium, not by the matter within the medium moving from one place to another.
As in ocean waves, high points are crests and low points are troughs. Amplitude is the distance from the
midpoint to the crest (or trough) of a wave. The amplitude is equal to the maximum distance from equilibrium
(midpoint). In the diagram below, equilibrium is represented by the dashed line.
The wavelength of a wave is the distance between identical points from one wave to another. For example, in
the diagram above the wavelength is measured from the crest of the first wave to the crest of the second wave.
It is also measured from the point of the first wave to the identical point of the second wave. Disturbances
within mediums are caused by vibrations. Vibrations are periodic motion. The source of all waves is something
that vibrates. The frequency of a wave describes how often these vibrations occur. The number of back-andforth vibrations that occur in each amount of time represents the frequency of the wave, with time measured in
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seconds. In the example above, the ball dropping and the bouncing back up from the spring would represent one
cycle. If this occurred in one second, then the frequency would be one hertz (Hz). The unit of frequency is
called the hertz and represents the number of cycles per second. Therefore, the frequency of one cycle per
second would equal 1 hertz, the frequency of 2 cycles per second is 2 hertz, and so on. Higher frequencies can
be measured in kilohertz (kHz thousands of hertz), megahertz (mHz millions of hertz), or gigahertz (gHz
billions of hertz). For example, AM radio waves are broadcasted in kilohertz, FM radio waves are broadcasted
in megahertz, and your home microwave oven operates off gigahertz.
1. What is the difference between the amplitude and wavelength of a wave?
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2. How is the frequency of a wave measured?
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What are Types of Wave Motion?
Whenever a disturbance causes motion within a medium that travels at right angles (perpendicular) to the
direction the wave is moving, it is called a transverse wave. A transverse wave is demonstrated in the figure on
the previous page by the ball and spring bouncing up and down, and in the figure below by shaking the coiled
spring up and down. Light and radio waves are examples of transverse waves.
Not all waves are transverse. Sometimes the particles in a medium move back and forth in the direction the
wave is traveling. When particles in a medium move along the direction of the wave it produces a longitudinal
wave. A longitudinal wave can be seen in the figure above as the coiled spring is pushed back and forth. Sound
waves are an example of a longitudinal wave.
3. Distinguish between a transverse wave and a longitudinal wave.
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What is Wave Interference?
Multiple waves can exist at the same time in the same space. Waves
can overlap to form an interference pattern. Within the pattern wave
effects can be increased, decreased, or neutralized. For example, when
rain falls on a pond or in a puddle, it produces multiple circular wave
patterns that overlap. This can be seen in the picture to the right. When
the crest of one wave overlaps the crest of another, the effects are
added together causing an increase in amplitude or reinforcing it. This
is constructive interference. When the crest of one wave overlaps the
trough of another, the effects are reduced. This is destructive
interference, or cancellation. Notice the reinforcement and
cancellation from wave interference in the figure below.
4. How does interference occur in waves?
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What is a Standing Wave?
If you tie a rope to a pole and shake the end up and down, it will
produce a wave with the rope. The wave is deflected from the pole
back along the rope to you. By shaking the rope, you can cause the
original and reflective waves to form a standing wave. A standing
wave is where part of the wave remains stationary and the wave
appears not to be traveling. The part of the wave that remains
stationary is called a node. In contrast, the parts of the wave with the
largest amplitudes are known as antinodes. Antinodes occur halfway
between nodes. Standing waves result from interference when two
waves of equal amplitude and wavelength pass through each other in
opposite direction. In the diagram to the right the nodes are
represented by the letter “N” and the antinodes are represented by the
letter “A”.
5. What causes a standing wave?
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Adapted from Hewitt, Paul G. “Chapter 25: Vibrations and Waves.” Conceptual Physics: the High School Physics Program, Pearson/Prentice Hall, 2006, pp. 372–386.
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Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Introduction to Waves (2:52)

“Physics – Waves – Introduction”. YouTube. Expertmathstutor, 2 Jan. 2014. Web.
What are waves in physics? This video goes over the basics of the different
types of waves as well as their properties.
Properties of Waves (3:58)
https://www.youtube.com/watch?v=xkQdQzIT9zU
“P1: Properties Of Waves (Revision).” YouTube. The GCSE Guide, 23 Nov. 2015. Web. 19 Feb. 2016.
What are the properties of waves? This video is an illustrated guide to the
properties of waves. It includes explanation of wave speed, amplitude, and
frequency in both longitudinal and transverse waves.
Wave Interference (5:32)

“Wave Interference.” YouTube. CrashCourse, 23 Aug. 2012. Web.
How do waves interact with each other? This video will give examples of
constructive and destructive interference when two waves meet.
Standing Waves on a String (3:24)

“Standing Waves Generated by String Vibration”. YouTube. ToneSpectra.com, 24 Jan. 2011. Web.
How are standing waves generated? This video gives an example of standing
waves that you can see. These are generated by a machine spinning a string at a
very high speed.
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Elaborate
Simulating Wave Interference
What happens when two waves meet while travelling through the same medium? What effect will the meeting
of the waves have upon the appearance of the medium? Will the two waves bounce off each other upon meeting
(much like two ping pong balls would) or will the two waves pass through each other? These questions relate to
the topic of wave interference.
Wave interference is a phenomenon that occurs when two waves meet while traveling along the same medium.
The interference of waves causes the medium to take on a shape that results from the total effect of the two
individual waves. To begin your exploration of wave interference, consider two pulses of the same amplitude
traveling in different directions along the same medium. As the pulses move towards each other, there will
eventually be a moment in time when they meet. In this computer simulation, you will explore what happens
when wave interference occurs.
Procedure:
1. Open the simulation “Wave Interference 2”:
http://zonalandeducation.com/mstm/physics/waves/interference/waveInterference2/WaveInterference2.h
tml
2. Observe the simulation. The red wave is labeled as “wave 1” and the blue wave is labeled as “wave 2”.
The white wave is the sum of the red wave plus the blue wave when interference occurs.
3. Click “You” toward the bottom of the simulation. This will give you control.
4. Click on the waves and use your mouse to move them back and forth.
5. Use the simulation to answer the questions on the next page.
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Analysis:
1. Slide the waves so that the red and blue waves overlap. This is an example of constructive interference.
What happens to the white wave during this constructive interference?
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2. Explain why this happens with the white wave.
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3. Slide the waves so that the crest of the red wave is directly over the trough of the blue wave. This is an
example of destructive interference. What happens to the white wave during this destructive
interference?
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4. Explain why this happens to the white wave.
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“Interference of Waves.” Waves – Lesson 3 – Behavior of Waves. The Physics Classroom, n.d. Web. 23 Feb. 2016.
http://www.physicsclassroom.com/class/waves/Lesson-3/Interference-of-Waves.
“Wave Interference 2.” Wave Interference 2 | Zona Land Education, Zona Land Education,
zonalandeducation.com/mstm/physics/waves/interference/waveInterference2/WaveInterference2.html.
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Evaluate
Review Questions
Answer the following questions.
1. As waves pass by a duck floating on a lake, the duck bobs up and down but remains in one place.
Explain why the duck is not carried along by the wave.
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2. Is the wave from question 1 a transverse or a longitudinal wave?
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3. On the diagram below, label the nodes and antinodes.
0m
2m
4m
6m
4. Explain how constructive interference is different from destructive interference.
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LESSON 5.2: ELECTROMAGNETIC WAVES
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Learning Goals for this Lesson
 Describe what electromagnetic waves are.
 Identify technology that utilizes different sections of the electromagnetic spectrum.
 Explain how electromagnetic waves transfer energy.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Electromagnetic Spectrum Concept Map
 Review Questions
Engage
Connect to Prior Knowledge
How do television stations broadcast live video across the entire world simultaneously?
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Explore
Exploration Activity
Visible light comes from energy that is given off by accelerating electric charges. Visible light is part of the
electromagnetic spectrum, seen in the diagram below. The electromagnetic spectrum is the range of
electromagnetic waves extending from radio waves to gamma rays. Electromagnetic waves carry energy and
are emitted by vibrating electric charges. You are familiar with these waves in everyday life. Light, radio
signals, and x-rays are all types of electromagnetic waves. The difference between these waves is in their length
and frequency.
Netting, Ruth. “The Electromagnetic Spectrum – Index Page.” The Electromagnetic Spectrum – Index Page. NASA, 25 Feb. 2011. Web. 22 Feb. 2016.
Electromagnetic waves are classified by the amount of energy they carry. This amount of energy determines
their wavelength and frequency. Higher energy waves such as gamma and x-rays have a higher frequency and
shorter wavelength, whereas lower energy waves such as radio waves have a lower frequency and longer
wavelength. The visible light you observe with your eyes lies towards the middle of these values.
Use the diagram to answer the following questions.
1. Which type of wave has the longest wavelength and lowest frequency?
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2. Which type of wave has the shortest wavelength and highest frequency?
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3. Which has a longer wavelength, infrared or ultraviolet light?
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4. What type of wave has a wavelength that is approximately the size of a bee?
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What are Electromagnetic Waves?
Visible light is a small portion of the electromagnetic spectrum. The electromagnetic spectrum shows the
range of different types of electromagnetic waves. This includes familiar types such as radio waves,
microwaves, and x-rays. As the wavelength along the electromagnetic spectrum decreases, frequency increases.
This is illustrated in the diagram below.
Visible light is the electromagnetic waves we can see. The lowest frequency of light we can see with our eyes
appear red and the highest appear violet. Electromagnetic waves with frequencies below red visible light are
known as infrared. Objects that give off heat also emit infrared waves. You can feel infrared waves as warmth
on your skin. Infrared waves are also used in television remote controls and burglar alarms. Electromagnetic
waves with frequencies above the violet visible light are known as ultraviolet. Ultraviolet waves are
responsible for sunburns and are used in tanning bed lamps. Ultraviolet light is also used as a disinfectant to kill
bacteria and to harden gel nail polish.
Radio waves have the longest wavelength and the smallest frequency of the electromagnetic spectrum.
Because these waves are so large, they are good for transmitting information for long distances. Microwaves
are part of the radio spectrum. They are used for communication purposes and in your home microwave oven to
heat up food. Microwave towers are used to transmit telephone calls and computer data. Shorter wavelength
microwaves are used for radar. X-rays have very short wavelengths and very large frequencies.
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They are usually thought of in terms of their energy, not their wavelength. X-rays are used in medicine and
dentistry. Airport security also uses x-rays to see inside baggage. Gamma rays are the shortest wavelength
electromagnetic waves and have the largest frequency. Like x-rays, gamma rays are usually described in terms
of energy rather than wavelength. Gamma rays are produced by radioactive atoms and nuclear explosions.
Gamma rays can kill living cells. They are used in medicine to destroy cancer cells.
1. Rank the following types of electromagnetic waves from longest wavelength to shortest: x-rays, gamma
rays, microwaves, ultraviolet light, infared light, visible light, radio waves.
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2. Why are radio waves good for transmitting information long distances?
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3. Which color of the visible spectrum has the lowest frequency? Which color has the highest frequency?
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Adapted from Serway, Raymond A., and Jerry S. Faughn. “Chapter 20: Electromagnetic Induction/Section 4: Electromagnetic Waves.” Holt McDougal Physics, Holt
McDougal, 2012, pp. 715–721.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
The Electromagnetic Spetrum (5:19)

“The Electromagnetic Spectrum.” YouTube. The Science Channel, 1 Aug. 2010. Web. 22 Feb. 2016.
What is the electromagnetic spectrum and how is it used? This video will explain in
detail the different types of electromagnetic waves.
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Elaborate
Electromagnetic Spectrum Concept Map
Using the following terms, complete the concept map below to show how different electromagnetic waves of
the electromagnetic spectrum are utilized. Each term is found in the reading section for this lesson.
Electromagnetic Waves
Visible Light
Gamma Rays
Microwaves
Ultraviolet Light
X-rays
Used to destroy cancer
cells
Infrared
Radio Waves
The cause of sunburns
The electromagnetic spectrum
contains 7 categories of
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The wavelength
of light humans
can see ranging
from red to
violet
Transmit information
long distances
Given off by
anything warm
Used for airport security
to view inside luggage
Used to cook food and to
transmitted telephone calls
and computer data
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Evaluate
Review Questions
Answer the following questions.
1. What is the source of electromagnetic waves?
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2. Give an example of an electromagnetic wave that is used to transmit information. How is it used?
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3. Give an example of an electromagnetic wave that is used in medicine. How is it used?
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4. Which electromagnetic waves do you encounter daily? Explain how you encounter these electromagnetic
waves.
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5. Think of an example in which another person may not encounter the same electromagnetic waves as you.
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LESSON 5.3: ELECTROMAGNETIC RADIATION
Learning Goals for this Credit
Communicate scientific information clearly, thoroughly and accurately.
Learning Goals for this Lesson
 Recognize electromagnetic radiation as a form of thermal transfer.
 Predict thermal absorption of electromagnetic radiation of different surfaces.
 Relate thermal radiation and absorption to real world situations.
Lesson Assignments
 Connect to Prior Knowledge
 Exploration Activity
 Reading and Questions
 Videos (optional)
 Roof Color and Temperature
 Constructed Response
Engage
Connect to Prior Knowledge
When you are outside what colors of clothing make you feel warm? Why do you think that is?
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Explore
Exploration Activity
All hot objects emit electromagnetic radiation, but the precise frequency
and wavelength of that radiation depends on the temperature of the object.
Think about a hot lump of coal. The coal will emit a wide range of
wavelengths – some visible, some ultraviolet and some infrared. At high
temperatures, there will be a large amount of energy and much of this will
be emitted in the visible part of the spectrum. As the coal cools there will
be less total energy emitted per second, less visible light and more
infrared. When the temperature has fallen still further, the coal will only
emit infrared – on a dark night you would not be able to see it.
The graph in Figure 1 shows how the energy emitted per second by a hot object varies with wavelength and
frequency. There are two lines on the graph – one shows an object at high temperature and the other the same
object after it has cooled down. (Remember that a long wavelength means low frequency. A long wavelength is
at the right hand side of the graph and high frequency at the left hand side). Notice how the area under the
lines changes from when the object is hot to when it is cool, and also how the position of the wavelength where
most energy is emitted per second moves towards the long wavelength side.
Adapted from Gibbs, Kieth. “The Wavelength and Temperature of Electromagnetic Radiation.” Wave Properties: Wave Length. Schoolphysics, 2013. Web. 23 Feb.
2016. .
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Use the graph from the previous page to answer the questions below.
1. At the highest energy level for a high temperature, which colors are likely to be seen?
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2. At the highest energy level for a low temperature, which colors are likely to be seen?
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3. What color would you expect to have the highest temperature? Which would have the lowest?
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4. Which would you expect to have a higher temperature: a burning piece of coal that is white or a burning
piece of coal that is red?
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Explain
As you complete the reading, answer the questions in the space provided.
Reading
What is Heat Transfer?
All of the energy (radiation) that reaches Earth comes from the sun. Intercepted by Earth’s atmosphere, a small
percentage of the sun’s energy is absorbed directly by certain gases, such as ozone and water vapor. Some
energy is reflected to space by clouds and the Earth’s surface. Most of the sun’s energy, however, is absorbed by
Earth’s surface.
Energy is transferred between the Earth’s surface and
the atmosphere in a variety of ways, including
radiation, conduction, and convection. The graphic to
the right uses a camp stove to summarize the various
mechanisms of heat transfer. If you were standing next
to the camp stove, you would be warmed by the
radiation emitted by the stove’s gas flame. A portion of
the radiant energy generated by the gas flame is
absorbed by the frying pan and the pot of water. By the
process of conduction, this energy is transferred
through the pot and pan. If you reached the metal
handle of the frying pan without using a potholder, you
would burn your fingers! As the temperature of the
water at the bottom of the pot increases, this layer of
water moves upward and is replaced by cool water
descending from above. As a result, convection
currents that redistribute the newly acquired energy
throughout the pot are established.
As in the camp stove example, the heating of the Earth’s atmosphere involves radiation, conduction, and
convection, which occur simultaneously. A basic tenet of meteorology is that the sun warms the ground and the
ground warms the air. Energy from the sun is the driving force behind weather and climate, and ultimately life
on Earth.
1. How is Earth’s atmosphere heated?
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What is Radiation?
What do trees, snow, cars, horses, rocks, centipedes, oceans, Earth’s atmosphere, and you have in common?
Each one is a source of radiation to some degree. Most of this radiation is invisible to humans but that does not
make it any less real.
Radiation is the transfer of heat energy by electromagnetic wave motion. The transfer of energy from the sun
across nearly empty space is accomplished primarily by radiation. Radiation occurs without the involvement of
a physical substance as the medium. The sun emits many forms of electromagnetic radiation in varying
quantities. About 43% of the total radiant energy emitted from the sun is in the visible parts of the spectrum.
The bulk of the remainder lies in the near-infrared (49%) and ultraviolet section (7%). Less than 1% of solar
radiation is emitted as x-rays, gamma waves, and radio waves.
A perfect radiating body emits energy in all wavelengths, however, the wave energies are not emitted equally in
all wavelengths; a spectrum will show a distinct maximum in energy at a particular wavelength depending upon
the temperature of the radiating body. As the temperature increases, the maximum radiation occurs at shorter
and shorter wavelengths. The hotter the radiating body, the shorter the wavelength of maximum radiation. For
example, a very hot metal rod will emit visible radiation and produce a white glow. On cooling, it will emit
more of its energy in longer wavelengths and will glow a reddish color. Eventually no light will be emitted, but
if you place your hand near the rod, the infrared radiation will be detectable as heat. The amount of energy
absorbed by an object depends upon the following:


The object’s absorptivity, which, in the visible range of wavelengths, is a function of its color.
The intensity of the radiation striking the object.
Darker-colored objects absorb more visible radiation, whereas lighter-colored objects reflect more visible
radiation. That is why you usually choose light-colored clothing on hot days. Every surface on Earth absorbs
and reflects energy to varying degrees, based on its color and texture.
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2. What is radiation?
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3. Would a glowing rod be hotter if it were white or red? Why?
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4. The amount of light energy absorbed by an object depends on what two factors?
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Adapted from “Atmospheric Processes – Radiation.” Introduction to the Atmosphere. NCAR & UCAR, n.d. Web. 22 Feb. 2016.
.
Videos
If you would like to learn more about this topic, watch the videos below for more information. (Optional)
Is Blue Hotter Than Red? (3:04)
https://www.youtube.com/watch?v=lvSHCUvasdU
“Is Blue Hotter than Red?” YouTube. YouTube, 28 July 2014. Web. 22 Feb. 2016.
What colors are hottest? This video will explain how color and temperature are related.
White vs. Green Roofs (1:03)
https://www.youtube.com/watch?v=08bwUBMqrtk
“White Roofs Are Better for the Environment Than Green Roofs” YouTube. GeoBeats News, 29 Jan. 2014. Web.
Which type of roofs are more cost effective for cooling? This video makes the case for
white roofs over those covered with plants.
Weighing the Benefits of Green Roofs (9:29)

“Weighing the Benefits of Green Roofs.” YouTube. Wall Street Journal, 6 Oct. 2008. Web.
What are some of the advantages of green roofs besides heat reduction? What
outcomes are the scientists studying?
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Elaborate
Roof Color and Temperature
Urban Heat Islands
Cities maintain hotter temperatures
than areas with less human
infrastructure. There are many
contributing factors, such as tall
buildings blocking wind, pollutants
released into the air, and the heat given
off by machines. One factor that you
have explored is the amount of heat
certain surfaces can absorb due to their
color and composition. Traditionally,
many roofs were black or other darker
colors, which absorbed large amounts
of solar radiation. The following three articles contain varied views of how you can modify the roofs of
buildings and homes to reduce the amount of heat they absorb. Read the articles and then respond to the prompt
below.
Article 1: Beating the Heat
When it comes to heat waves, Stuart Gaffin considers himself pretty lucky. An associate research scientist with
the Earth Institute at Columbia University, Gaffin frequently studies heat waves. So far, however, he has
managed to avoid getting caught in a deadly one, such as the Chicago heat wave of 1995 or the Paris heat wave
of 2003. He lives in New York City and the worst heat wave he remembers struck when he was in a nearby
rural area. “We had no air conditioning, and it was so bad, it was like 106 degrees Fahrenheit,” he recalls. He
left the countryside and rushed back to the city where his air-conditioned apartment awaited.
He admits the move was a little ironic. Ironic because Gaffin also studies what’s known as the urban heat
island—the tendency of cities to experience warmer temperatures than surrounding rural and suburban areas. In
leaving the countryside, he actually headed for a hotter environment. Gaffin’s New York City apartment has air
conditioning, but “we have a lot of poor communities in New York with low air conditioning rates,” he says.
And electricity blackouts caused by a surge in demand during heat waves can catch anyone. “The heat wave
problem is a real one, and one of the primary reasons to look at urban heat islands,” he explains.
Anyone who has ever planned to spend hours outside on a hot, sunny day has probably heard the advice to wear
light colors. Pale colors reflect much of the sun’s light, keeping their wearers cool. The same is true for
buildings. Gaffin and his colleagues presented the results of their 2002 New York City heat wave study at a
science meeting in January 2006, and at that time, he considered white roofs the winning strategy. By April
2006, however, he had changed his mind.
The study in New York confirmed that white roofs—generally made with the use of a thin, light coating—
absorb much less of the sun’s energy than asphalt roofs, and they are fairly inexpensive and easy to install.
However, even though white surfaces may be cooler than dark surfaces, they still trap heat. “Just go around
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your neighborhood. I think you’ll find that lighter urban surfaces are still pretty hot in the summer, compared to
plants,” Gaffin says. What’s worse, “in urban settings, white roofs get dirty quickly,” reducing their ability to
reflect sunlight. Even when they’re kept clean, white roofs cause problems, he explains. In reflecting the
sunlight, they may just bounce much of it off nearby buildings, heating up the immediate area. “You haven’t
really gotten the light out of the city,” he says. And in the wintertime, light roofs may cool buildings
unnecessarily, increasing heating demands.
Light-colored roofs held another drawback for Gaffin. As he researched mitigation options for the urban heat
island, he became aware of another issue that causes some cities as much hardship: storm water runoff. “The
purpose of asphalt is to create an impervious surface,” he explains, to keep out water. Unfortunately, the water
that can’t be absorbed by roofs and roads has to go somewhere else.
To deal with runoff from heavy rains, cities have storm sewers, but many cities use the same systems to handle
both the overflow from rainstorms and the water flushed out of toilets. Heavy rains can overwhelm these
systems (called combined sewer overflows), pushing raw sewage into waterways. “It’s the major source of
pathogens in the New York Harbor. It’s a major problem in Europe. This is one of the impediments to ever
reclaiming the recreational and other values of our urban water systems,” he says. He has coined a term for this
problem, as a parallel to the urban heat island. He calls it “the urban runoff island.” Light-colored roofs might
absorb less of the Sun’s energy than dark roofs, he says, but they do nothing to mitigate runoff. “I’m no fan of
white roofs anymore,” Gaffin concludes. “I started this line of research thinking they should be promoted. I
finished this research thinking they are a secondary option.” Gaffin would rather promote a solution that
addresses both urban heat and urban runoff. If cities don’t have much room for lots of additional trees, and if
light-colored roofs only partially reduce urban heat and in no way reduce runoff, just one option remains:
vegetation-covered roofs.
Vegetation-covered roofs typically include the following layers: a waterproof membrane at the bottom, a layer
of drainage materials, a root-repellant and filter layer, a lightweight soil-like growing medium, and finally the
plants. Compared to standard roofs, green roofs do have more mass, but thin systems of only 3 to 4 inches (7.5
to 10 centimeters) are sufficient. When they are saturated with rainwater, they may create a load of 1,197
pascals (about 25 pounds per square foot), which is often feasible for many city buildings. By evaporating
moisture, the plants release heat without raising local temperatures. Likewise, the plants and soil soak up
rainfall like a sponge instead of letting it roll right off the surface.
Scott, Michon. “Beating the Heat in the World’s Big Cities : Feature Articles.” Beating the Heat in the World’s Big Cities : Feature Articles. NASA, 1 Aug. 2006. Web.
22 Feb. 2016. .
Article 2: How to Decide Between a White or Green Roof?
Black roofs are out, and white and green roofs are in. However, which environmentally friendly option gives
you the most bang for your buck?
Roofing has become an environmental and public health issue in cities because commonly used dark roofs
absorb sunlight, heating the building and driving up air-conditioning use and heat-related deaths. In contrast,
white roofs reflect sunlight and green roofs covered with plants insulate the building from heat. The authors of a
new report in Energy and Buildings set out to tally the economic advantages and disadvantages of white and
green roofs. First, they note that green roofs don’t reflect sunlight as well as white roofs. White roofs are about
three times better at cooling the planet than green roofs, the team estimates.
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The researchers then studied the costs involved in installing, maintaining, and replacing each type of roof over
50 years. They also accounted for benefits such as the money saved from lowering AC use, reduced greenhouse
gas emissions from power plants, global cooling, and improving storm water management.
Green roofs cost more to install, and they require owners to tend to the plants, particularly as the gardens are
first becoming established. On the other hand, white roofs actually perform worse on energy savings because
although they’re good at cooling buildings in the summer, they can drive up heating bills in the winter.
Overall, green roofs cost about $96 per square meter more than white roofs over 50 years, the team concludes.
However, the cost difference per year is “sufficiently small that the choice between a white and green roof
should be based on preferences of the building owner,” the authors write. The analysis didn’t account for other
benefits of green roofs, such as offering natural habitat patches. “Owners concerned with global warming
should choose white roofs,” they advise, while those “concerned with local environmental benefits should
choose green roofs”.
Kwok, Roberta. “How to Decide between a White or Green Roof – Conservation.” Conservation RSS. University of Washington, 28 Jan. 2014. Web. 22 Feb. 2016.
.
Article 3: White, Green or Black Roofs?
A green roof, often called vegetated roofs or rooftop gardens, has become an increasingly popular choice for
aesthetic and environmental reasons. Rosenfeld acknowledges that their economic analysis does not capture all
of the benefits of a green roof. For example, rooftop gardens provide storm water management, an appreciable
benefit in cities with sewage overflow issues, while helping to cool the roof’s surface as well as the air. Green
roofs may also give building occupants the opportunity to enjoy green space where they live or work. “We
leave open the possibility that other factors may make green roofs more attractive or more beneficial options in
certain scenarios,” said Mandel, a graduate student researcher at Berkeley Lab. “The relative costs and benefits
do vary by circumstance.”
However, unlike white roofs, green roofs do not offset climate change. White roofs are more reflective than
green roofs, reflecting roughly three times more sunlight back into the atmosphere and therefore absorbing less
sunlight at earth’s surface. By absorbing less sunlight than either green or black roofs, white roofs offset a
portion of the warming effect from greenhouse gas emissions. “Both white and green roofs do a good job at
cooling the building and cooling the air in the city, but white roofs are three times more effective at countering
climate change than green roofs,” said Rosenfeld.
Chao, Julie. “White, Green or Black Roofs? Berkeley Lab Report Compares Economic Payoffs | Berkeley Lab.” News Center. Cal State Berkley, 21 Jan. 2014. Web. 22
Feb. 2016. .
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Evaluate
Constructed Response
How do you think we should be building roofs on our structures? In the space below write a one paragraph
(minimum 5 sentences) response explaining which type of roof you would prefer. Use evidence from the three
articles, along with your knowledge of solar radiation to justify your position.
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Revisit the essential question. Did your answer change? Why or why not?
Essential Question
How do invisible things such as sound and Wi-Fi internet travel from place to place?
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