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Electromagnetic Spectrum

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It’s a warm sunny Saturday, and Michael and Lavar have a big day planned. They’re going to ride across town to meet their friends and then go to the zoo. The boys may not realize it, but they will be bombarded by electromagnetic radiation as they ride their bikes and walk around the zoo grounds. 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.

Q: Besides visible light and infrared light, what other kinds of electromagnetic radiation will the boys be exposed to in sunlight?

A: Sunlight consists of all the different kinds of electromagnetic radiation, from harmless radio waves to deadly gamma rays. Fortunately, Earth’s atmosphere prevents most of the harmful radiation from reaching Earth’s surface. You can read about the different kinds of electromagnetic radiation in this article.

Electromagnetic Radiation

Electromagnetic radiation is energy that travels in waves across space as well as through matter. Most of the electromagnetic radiation on Earth comes from the sun. Like other waves, electromagnetic waves are characterized by certain wavelengths and wave frequencies. Wavelength is the distance between two corresponding points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Electromagnetic waves with shorter wavelengths have higher frequencies and more energy.

A Spectrum of Electromagnetic Waves

Visible light and infrared light are just a small part of the full range of electromagnetic radiation, which is called the electromagnetic spectrum . You can see the waves of the electromagnetic spectrum in the Figure below . At the top of the diagram, the wavelengths of the waves are given. Also included are objects that are about the same size as the corresponding wavelengths. The frequencies and energy levels of the waves are shown at the bottom of the diagram. Some sources of the waves are also given. For a video introduction to the electromagnetic spectrum, go to this URL: http://www.youtube.com/watch?NR=1&feature=endscreen&v=cfXzwh3KadE

  • On the left side of the electromagnetic spectrum diagram are radio waves and microwaves. Radio waves have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy.
  • On the right side of the diagram are X rays and gamma rays. They have the shortest wavelengths and highest frequencies of all electromagnetic waves. They also have the most energy.
  • Between these two extremes are waves that are commonly called light. Light includes infrared light, visible light, and ultraviolet light. The wavelengths, frequencies, and energy levels of light fall in between those of radio waves on the left and X rays and gamma rays on the right.

Q: Which type of light has the longest wavelengths?

A: Infrared light has the longest wavelengths.

Q: What sources of infrared light are shown in the diagram?

A: The sources in the diagram are people and light bulbs, but all living things and most other objects give off infrared light.

Summary

  • Electromagnetic radiation travels in waves through space or matter. Electromagnetic waves with shorter wavelengths have higher frequencies and more energy.
  • The full range of electromagnetic radiation is called the electromagnetic spectrum. From longest to shortest wavelengths, it includes radio waves, microwaves, infrared light, visible light, ultraviolet light, X rays, and gamma rays.

Vocabulary

  • electromagnetic spectrum : Full range of wavelengths of electromagnetic waves, from radio waves to gamma rays.

Practice

At the first URL below, read about electromagnetic waves with different frequencies. Then use the information to complete the table at the second URL. http://www.darvill.clara.net/emag/index.htm and http://www.darvill.clara.net/emag/gcseemag.pdf

Review

  1. Describe the relationship between the wavelength and frequency of electromagnetic waves.
  2. What is the electromagnetic spectrum?
  3. Which electromagnetic waves have the longest wavelengths?
  4. Identify a source of microwaves.
  5. Which type of light has the highest frequencies?
  6. Explain why gamma rays are the most dangerous of all electromagnetic waves.

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