Resonance Rings

Description: Different sized rings demonstrate the relationship between the frequency of electromagnetic radiation and atmospheric absorption.

Objective: To show how atoms and molecules in Earth's atmosphere absorb energy through resonance.


Materials:

Used lightweight file folders
Cardboard sheet about 20 by 30 cm
Masking tape
Scissors

Procedure:

1. Cut two strips of paper from used file folders. Each strip should be 3 cm wide. Make the strips approximately 30 and 35 cm long.

2. Curl each strip into a cylinder and tape the ends together.

3. Tape the cylinders to the cardboard as shown in the diagram. If the ring has a crease from the file folder, the crease should be at the bottom.

4. Holding the cardboard, slowly shake it back and forth and observe what happens when you gradually increase the frequency of the shaking.

Discussion:

All objects have a natural frequency at which they vibrate. When the frequency of the shaking matches the frequency of one of the rings in this activity, it begins to vibrate more than the rest. In other words, some of the energy in the shaking is absorbed by that ring. This effect is called resonance. Resonance takes place when energy of the right frequency (or multiples of the right frequency) is added to an object causing it to vibrate. When electromagnetic radiation enters Earth's atmosphere, certain wavelengths match the natural frequencies of atoms and molecules of various atmospheric gases such as nitrogen

and ozone. When this happens, the energy in those wavelengths is absorbed by those atoms or molecules, intercepting this energy before it reaches Earth's surface. Wavelengths that do not match the natural frequencies of these atmospheric constituents pass through. (See figure 2 on page 25.)

Resonance is important to astronomy for another reason. All starlight begins in the center of the star as a product of nuclear fusion. As the radiation emerges from the photosphere or surface of the star, some wavelengths of radiation may be missing. The missing components produce dark lines, called absorption lines, in the star's spectra. The lines are created as the radiation passes through the outer gaseous layers of the star. Some of that radiation will be absorbed as various gas atoms present there resonate. Absorption lines tell what elements are present in the outer gaseous layers of the star.

For Further Research:

  • Investigate the natural frequencies of various objects such as bells, wine goblets, and tuning forks. If you have an oscilloscope, use it to convert the sounds to wave forms.
  • Why has the playing of the song "Louie, Louie" been banned at several college football stadiums? Why do marching soldiers crossing a bridge "break cadence"?
  • What gas in Earth's upper atmosphere blocks ultraviolet radiation? Why is it important?

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Last modified prior to September, 2000 by the Windows Team

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