The electromagnetic spectrum describes the range of electromagnetic waves placed in order of increasing frequency. At one end of the spectrum are radio waves, which have a very low frequency and long wavelengths. At the other end of the spectrum are high-frequency (short wavelength) gamma rays. All electromagnetic waves travel at the same speed - the speed of light. They differ in the amount of energy they transfer, called electromagnetic radiation. Lower-frequency waves like radio waves emit less electromagnetic radiation than do higher-frequency rays like gamma rays.
In this lesson, students explore various types of electromagnetic waves. They watch a video segment and use an interactive activity that both explain the range of the spectrum and common sources of electromagnetic waves. They also view images of astronomical objects that were observed with telescopes designed to detect different forms of electromagnetic radiation. They then watch two more video segments that explain more about the physics of electromagnetic waves, including the scientific theory that couples electricity and magnetism, which is the fundamental principle behind electromagnetic radiation.
- Understand that there are different types of electromagnetic waves, including radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays
- Understand that we experience natural electromagnetic radiation from the sun and from terrestrial sources, and human-made electromagnetic radiation from sources such as cell phones, microwave ovens, and power lines
- Understand that astronomical objects emit electromagnetic radiation at all frequencies and by observing objects at different frequencies their structure and phenomena can be understood more deeply
- Understand that electromagnetic waves are the result of a disturbance of electric and magnetic fields
Grade Level: 9-12
- Three class periods
- The Electromagnetic Spectrum: NASA Video
- Astronomical Images in Different Wavelengths Interactive
- Tour the Electromagnetic Spectrum Interactive
- The Electromagnetic Spectrum: FRONTLINE Video
- String Theory: A New Picture of Gravity Video
- Electromagnetic Spectrum Data Table (PDF) handout (PDF)
- Electromagnetic Spectrum Diagram Image
- Large sheet of chart paper (2-3 feet wide on a roll)
- Magazines with photos of common household objects such as radios, microwaves, TVs
- Astronomy magazines with images observed at various wavelengths using space-based and Earth-based telescopes
Part I: The Universe at Multiple Frequencies
1. Begin a class discussion about various forms of electromagnetic radiation. If students have prior knowledge of electromagnetic waves, such as radio waves, visible light, and X-rays, have them sketch a chart on the board that shows the relative position of each form of radiation along an axis of increasing (or decreasing) frequency, wavelength, or energy. Then ask for examples of objects that emit radiation at each frequency. Take this informal discussion as far as you can. If students have no prior knowledge in this area, move directly to the next steps.
2. Show the The Electromagnetic Spectrum: NASA video to give students an overview of electromagnetic radiation. Have students work with theAstronomical Images in Different Wavelengths interactive activity and discuss how the images of each object differ when observed at different parts of the electromagnetic spectrum. Ask:
- Why do astronomers build radio telescopes and X-ray telescopes, in addition to the optical telescopes with which most people are familiar?
Part II: Creating An Electromagnetic Spectrum Chart
3. Have students work through the Tour the Electromagnetic Spectrum interactive activity. Have them discuss the various regions of the spectrum and common objects that utilize radiation at each frequency/wavelength.
4. Have students work as a class to make an Electromagnetic Spectrum chart that runs the length of a classroom wall. Have them draw a horizontal axis along the bottom of the chart and label it with the different types of radiation and their corresponding range of wavelengths and frequencies. (Start with radio waves at the left end of the axis). They may use the Electromagnetic Spectrum Data Table (PDF) handout as a guide in listing wavelength in either angstroms or centimeters. Be sure to record units using a scale of powers of ten (this is a logarithmic scale), so that the bandwidth of radio waves is noticeably greater than the bandwidth of the other forms, in particular, visible light, which makes up a tiny fraction of the spectrum. Use the sample Electromagnetic Spectrum Diagram to see how to set up the chart.
Options for the chart:
- List the range of energies associated with each wavelength.
- Draw a picture of one wavelength, or use an image of an object that is the size of a wavelength at each region of the spectrum.
- Add pictures of common sources of electromagnetic radiation for each region of the spectrum.
- Add astronomical images that are observed at each wavelength.
- Add pictures of the different types of telescopes that are used to observe radiation at each region of the spectrum.
5. Have students compare their completed chart with the one they drew at the beginning of the lesson, if applicable.
Part III: The Creation of Electromagnetic Waves
6. Have students watch the The Electromagnetic Spectrum: FRONTLINE video. Discuss how electromagnetic waves are created. Guide students toward discussing electric fields and magnetic fields that they experience every day.
7. Have students watch the String Theory: A New Picture of Gravity video. Discuss the connection between electric and magnetic fields. This maps nicely with a demonstration of Faraday's law or an electromagnet.
Check for Understanding
Have students discuss the following:
- What are the different regions of the electromagnetic spectrum? What do all electromagnetic waves have in common? How do they differ?
- What are some sources of electromagnetic radiation that we use every day?
- Give an example of when observing an object through different wavelengths provides significantly more information than an image of the object in only one type of electromagnetic radiation.