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 6-8 > Physical Science
 Grade level: 6-8 Subject: Physical Science Duration: Two or three class periods
 Objectives | Materials | Procedures | Adaptations | Discussion Questions | Evaluation | Extensions | Links | Academic Standards | Credit
Objective
Students will
• Understand that the sun’s energy is transferred to Earth by electromagnetic waves, which are transverse waves.
• Understand that there are eight main types of electromagnetic waves, classified on the electromagnetic spectrum according to their wavelengths.
• Understand how each of the types of electromagnetic radiation is used or found in our everyday lives.
Materials
For this lesson, you will need:
• Computer with Internet access
• Research materials on the electromagnetic spectrum (articles, books, textbook readings)
• Poster/picture of the electromagnetic spectrum
• Overhead projector, transparencies, and markers
• Chart paper
• Construction paper
• Magazines
• Scissors
• Bulletin board space in the classroom
• The Electromagnetic Spectrum Tutorial!
Procedures
1. Prior to this lesson, students should have an understanding of the two kinds of waves that exist in nature: compressional and transverse waves. They should be able to identify the characteristics of each wave and how they differ. Here are some important facts to know:

• Compressional waves – such as sound waves - require a medium to transfer energy.
• Transverse waves – such as light waves - can transfer energy in a vacuum, without a medium.
• Both types of waves are initiated by something that vibrates, but compressional waves travel slower than transverse waves.
• The sun’s energy reaches the Earth in transverse waves.
• The frequency and wavelength of a wave determines how much energy a wave has. Frequency is the number of wave crests that pass a point during one second. Wavelength is the distance between two identical points on two adjacent waves. The shorter the wavelength, the more energy the wave has. But as wavelength increases, frequency decreases.

Begin by asking students what they know about transverse waves and compressional waves. Work with students to create a t-chart on the board and compare and contrast the two types of waves. Identify key concepts associated with each wave. It may be helpful to create this chart on a transparency or chart paper for later reference and reinforcement.

2. Now draw a picture of the sun and the Earth. Ask students to describe how energy from the sun reaches the Earth. Draw transverse waves showing how electromagnetic energy is transferred from the Earth to the sun. Tell students that energy from the sun is called radiation. Write this term next to the word transverse waves on the illustration. Ask students in what context they have heard that word before. (For example, a radiator gives off heat, or radiation therapy is used to treat cancer.) Encourage students to use mnemonic devices to remember the concept of radiation as it relates to the sun’s energy. For example, students can use the sound “ray” in “radiation” to remind them of the sun’s rays warming their skin on a sunny day.

3. Explain to students that transverse waves that transfer radiation or energy are called electromagnetic waves. These waves are created by electrically charged particles that move. The terms “electromagnetic waves” and “electromagnetic radiation” are used interchangeably because the waves carry the sun’s radiation, which is composed of electrically charged particles. Refer back to the chart created at the beginning of class and ask students to come up with a list of possible characteristics of electromagnetic waves. Because they are transverse waves - and can travel in a vacuum — they can travel through space.

4. Explain to students that there are different types of electromagnetic radiation existing in the universe. One type of electromagnetic radiation is visible light. The electromagnetic spectrum is something scientists use to classify the different types of electromagnetic radiation. Show students a picture of the electromagnetic spectrum. Explain that, like the periodic table where elements are classified according to their structure, electromagnetic radiation is classified according to wavelengths and frequencies. Although there are different types of electromagnetic radiation, they all travel at the same speed - the speed of light or 186,000 miles per second. Humans are only able to see one small portion of the spectrum — visible light.

5. Send students to the Electromagnetic Spectrum Tutorial. Students will learn facts about each area of the spectrum, including where areas of the spectrum are found in the natural world and how areas are used in science, space exploration, communications, and medicine.

6. When students have returned from the tutorial, recap what they have learned. Explain that electromagnetic radiation is arranged in the spectrum from the longest wavelength to the shortest. Ask students to identify the waves with the longest and shortest wavelengths. (It may be helpful to draw wavelengths decreasing from left to right above a labeled diagram of the spectrum.) Based on what they have learned about frequency as it relates to wavelength (the longer the wavelength, the lower the frequency), ask students which waves have the lowest frequency and which have the highest frequency. It may be necessary to prompt them with some clues — the longer the wavelength, the lower number waves in a given space; the shorter the wavelength, the more waves there are in a given amount of space. One easy way for students to remember the relationship between frequency and wavelength is to consider that the longer the wavelength, the lower the frequency, emphasizing the ’l’ at the beginning of each word. And the shorter the wavelength, the higher the frequency, emphasizing the ’h’ in each word. (Again, it may be helpful to reinforce this relationship by labeling lower frequency by the radio waves on the spectrum and higher frequency by the gamma rays.)

7. Now explain to students that they will taking a closer look at one of the eight types of electromagnetic energy in the spectrum —radio waves, microwaves, infrared waves, visible light, ultraviolet light, x rays, gamma rays, and cosmic waves.

8. Divide the class into eight groups. Each group will focus on a portion of the electromagnetic spectrum assigned to them. Students should use traditional forms of research, for example reference books or class texts, as well as Internet links and the electromagnetic spectrum tutorial. Explain to students that groups must work together to research the following information about their form of radiation:

1. What are the characteristics of this type of radiation (wavelength, frequency, key facts)?
2. Where is this type of radiation located on the electromagnetic spectrum in relation to other kinds of radiation? What properties of the wave define why it is found within this area of the spectrum?
3. How is it used or found in our everyday lives or in certain industries? Identify and explain at least two uses.

4. Each member of the expert group must have the necessary information and materials to make a class presentation on their area of the spectrum. Encourage students to be creative in their presentations. Have a variety of materials for students to use for their presentations including construction paper, chart paper, markers, overheads, chalk board, colored chalk, and magazines. Tell students that the key to a successful and interesting presentation is to use visuals, such as labeled diagrams.

5. As students watch the presentations, have them complete a learning chart with important facts and questions about each type of radiation. Student learning charts may look like this:

 Type of Radiation Characteristic (wavelength, energy, frequency) Example of where it’s found or used My own question

6. As a final step, have students chose one question from their learning chart and research the answer.
Have students debate whether the federal government should be allowed to control the frequency bandwidths for communication. In the United States, radio and television stations emit two types of frequencies. In order for people to hear broadcasts, radio and television stations need to transmit along an audio frequency (AF) within the range of human hearing, which is 20 — 20,000 Hz. This audio frequency is transmitted along with a radio frequency that has been designated by the government. Radio frequencies distinguish each station. Some of the radio ranges designated by the Federal Communications Committee are:
AM radio: 530 — 1600 kHz
FM radio: 88-108 MHz
TV: 54-88 MHz (channels 2-6)
TV: 174-216 MHz (channels 7-13)
TV: ultra-high frequency (UHF), 470-890 MHz
Cellular telephones: 824 — 894 MHz.

The FCC also assigns ranges within radio and TV waves for use by airplanes, ships, police, military, cellular phone and amateur ham radio users The federal government restricts usage of specific bandwidths within radio frequency for military use only.

Before you begin the debate, have students familiarize themselves with frequency ranges currently in use. Students can access the US Frequency Allocation Charthttp://www.ntia.doc.gov/osmhome/allochrt.htmland the Federal Communications Committee Web site Charthttp://www.fcc.gov/to aid in their research. They should also research how other countries divide their “air wave” space. Students should consider any international implications of these designated ranges and find out what happens at the border between two different countries where the signals emitted by radio and television stations overlap.

Once all students have completed this preliminary work, divide the class into two debate groups. It is nice to let students choose their “side.” however, if the numbers are uneven, it may be necessary to split students evenly between both sides of the debate. Debate teams should present salient points to support their opinions. After the debate, ask the class as a whole to come to an agreement on whether it is better for the government or for private industry to “divvy up” the frequency ranges within the electromagnetic spectrum.

Discussion Questions
Use the following three-point rubric to evaluate students' work during this lesson.

1. Compare and contrast electromagnetic waves with other kinds of waves.
2. If radio waves are not compressional waves, like sound waves, explain what their role is in enabling us to hear music on our favorite radio station?
3. Thermograms are infrared photographs that show emission of infrared radiation emitted from objects. If you lived in a cold climate, how could a thermogram taken of your home be helpful to you as a homeowner?
4. Discuss why visible light is arranged into colors in the following order: red, orange, yellow, green, blue, indigo, and violet.
5. Debate what we could do to prevent exposure to ultraviolet radiation if the ozone layer continues to deteriorate.
6. Defend the importance of gamma rays in treating cancer, even though many patients suffer serious side effects to such treatment.
7. What type of electromagnetic radiation does a flame emit?
Evaluation
Visit each group as they research and create their presentations. Each student should help in the discussion and preparation. A 3-point rubric may be used to evaluate the content of the presentation.

• Three points:Students accurately and thoroughly address each of the three presentation questions. Visuals enhance the presentation.
• Two points:Students attempt to address each of the three questions with minor misunderstandings. Visuals are used, but may not enhance the presentation.
• One point:Students do not address all three questions. Those attempted are inaccurate with major misunderstandings.
Extensions
Our Electromagnetic Lives
Have students explore how their lives are affected by electromagnetic radiation by keeping an “electromagnetic journal” for one week. Ask them to record each time they observe or come in contact with electromagnetic radiation each day — such as listening to the radio, talking on their cordless phone, going through security at the airport, or getting a sunburn. Students should record the date, time, and a one-sentence explanation of the incident, including what type of electromagnetic radiation they observed. Have students share their encounters with electromagnetic radiation and create a class tally to find out the most popular daily activity involving exposure to electromagnetic radiation. Links
What is the Near-Earth Rendezvous Mission? [PDF]
Find information and additional activities on this topic at the Johns Hopkins Applied Physics Lab website.

An Exploration of the Planet Mercury [PDF]
Find information and additional activities on this topic at the Johns Hopkins Applied Physics Lab website.

Standards
Subject area:Science
Standard:
Understands energy types, sources, and conversions, and their relationship to heat and temperature.
Benchmarks:
Knows how the Sun acts as a major source of energy for changes on the Earth’s surface (i.e., the Sun loses energy by emitting light; some of this light is transferred to the Earth in a range of wavelengths including visible light, infrared radiation, and ultraviolet radiation)
Benchmark 9-12:
Knows that all energy can be considered to be either kinetic energy (energy of motion), potential energy (depends on relative position), or energy contained by a field (electromagnetic waves)