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# 21.4: Lesson 21.3 The Electromagnetic Spectrum

Difficulty Level: At Grade Created by: CK-12

## Key Concept

The electromagnetic spectrum is the full range of wavelengths and frequencies of electromagnetic radiation. Radio waves are the broad range of electromagnetic waves with the longest wavelengths and lowest frequencies. They include microwaves. Mid-wavelength electromagnetic waves are called light, which consists of infrared, visible, and ultraviolet light. X rays and gamma rays are the electromagnetic waves with the shortest wavelengths and highest frequencies. They are used in medicine and for other purposes.

## Standards

• MCR.6-8.SCI.9.4, 9
• NSES.5-8.B.3.6
• AAAS.6-8.4.E.5; AAAS.6-8.4.F.1, 2, 6, 9; AAAS.6-8.8.D.2; AAAS.6-8.12.D.4

## 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: full range of wavelengths of electromagnetic waves, from radio waves to gamma waves
• gamma ray: type of wave in the electromagnetic spectrum that has the shortest wavelength and greatest amount of energy
• infrared light: part of the electromagnetic spectrum in which waves have a wavelength between those of radio waves and visible light
• microwave: wave in the electromagnetic spectrum that falls at the upper range of radio waves
• radar: radio detection and ranging; use of reflected radio waves to track the position of objects
• radio wave: any wave in the electromagnetic spectrum that has a wavelength longer than infrared light
• ultraviolet light: electromagnetic radiation with a wavelength falling between the wavelengths of visible light and X rays
• visible light: range of wavelengths of electromagnetic waves that the human eye can detect
• X ray: wave in the electromagnetic spectrum with a wavelength between the wavelengths of ultraviolet light and gamma rays

## Teaching Strategies

### Introducing the Lesson

Write the names of the different wavelengths of electromagnetic radiation on the board in alphabetical order (gamma rays, infrared light, microwaves, radio waves, ultraviolet light, visible light, X rays). Then ask students to put the types of radiation in order based on wavelength, from longest wavelength (radio waves) to shortest wavelength (gamma rays). Students may not know the correct order at this point, so conclude by telling them they will learn the correct order—and why it matters—when they read this lesson.

### Activity

Have students work as a class to make an electromagnetic spectrum chart that runs the length of a classroom wall. You can provide them with a roll of butcher or craft paper for the chart (available at office supply stores). Students should draw a horizontal axis and label it with the different types of radiation and their corresponding range of wavelengths and frequencies. The bandwidths of the different types of waves should be approximately proportional to the bandwidths of the actual waves. You might also have students add the range of energies associated with each wavelength and pictures of common sources of electromagnetic radiation for each region of the spectrum.

### Discussion

Students can learn how different wavelengths in the electromagnetic spectrum are used in the U.S. by exploring the interactive chart at the first URL below. They are likely to be impressed by the number of different ways electromagnetic waves are used. After students have explored the chart, discuss with the class why the government regulates use of the electromagnetic spectrum. More information about the issue is available at the second URL below.

### Differentiated Instruction

Suggest that students take the self-guided tour of the electromagnetic spectrum at the following URL. It is a self-paced tutorial for beginners, and covers all seven sections of the spectrum, from radio waves through gamma rays. Each segment of the tutorial contains specific examples, photos, and naturally occurring sources of the waves. Students can learn more when they are ready by rolling the cursor over the examples.

### Enrichment

Ask a few students to create a song or rap about the electromagnetic spectrum that conveys basic information about the different wavelengths of radiation. If they need inspiration, suggest they listen to the teacher-created song at the following URL.

### Science Inquiry

Some students may be interested in how X rays and CAT scans make images of structures inside the body. Direct them to the excellent tutorial at the URL below.

### Science Inquiry

The URL below provides a self-directed interactive inquiry activity consisting of four modules. Students may work independently or in small groups to complete each module. They will investigate different concepts related to the electromagnetic spectrum by examining relationships among wavelength, color, and temperature. Then they will determine the temperature of a variety of stars found in images from the Hubble Space Telescope and other sources.

### Real-World Connection

Have students explore how their lives are affected by electromagnetic radiation by keeping an “electromagnetic journal” for a week. Ask them to record each time they observe or come in contact with any type of electromagnetic radiation. Examples might include listening to the radio, watching TV, making popcorn in a microwave oven, talking on their cell phone, or going through security at an airport. Students should record the date, time, and a one-sentence explanation of the incident, including which type of electromagnetic radiation was involved. At the end of the week, have students share their encounters with electromagnetic radiation and create a class tally to find out the most common activity involving exposure to electromagnetic radiation.

## Reinforce and Review

### Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

### Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

### Lesson Quiz

Check students’ mastery of the lesson with Lesson 21.3 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.

## Points to Consider

This chapter introduces visible light. The next 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, 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?)

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