Thursday, 10 February 2011

The Electromagnetic Spectrum: Waves Of Energy


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.

1 comment:

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