Wavelength and Energy

Description: Shaking a rope permits students to feel the relationship between wavelength, frequency, and energy.

Objective: To demonstrate the relationship between wave frequency and energy in the electromagnetic spectrum.


Materials:

Rope (50 ft. length of cotton clothes line)

Procedure:

1. Select two students to hold the rope. Have each student stand in an aisle or in opposite corners so that the rope is stretched between them.

2. While one end of the rope is held still, have the other student shake the opposite end up and down at a moderate but steady rate.

3. Ask the remaining students to observe the wave patterns created in the rope. Point out wave crests. Ask the students to estimate the wavelength and frequency of waves reaching the other student. The wavelength is the distance from wave crest to wave crest. Frequency is the number of waves reaching the far end of the rope each second.

4. Tell the student shaking the rope to shake it faster. Again estimate the wavelength and frequency.

5. Tell the student shaking the rope to shake the rope as fast as he or she can. Again, estimate the wavelength and frequency.

6. Stop the demonstration and ask the student shaking the rope if it is easier to produce low frequency (long wavelength) or high frequency (short wavelength) waves.

Discussion:

This activity provides a graphic demonstration of the relationship between energy and wavelength. High-frequency waves (short wavelength) represent more energy than low-frequency (long wave-length) waves.

For Further Research:

  • As time permits, let the remaining students try the rope demonstration.
  • A similar demonstration can be conducted with a coiled spring (Slinky).
  • Invite a hospital medical imaging specialist to talk to the class about the use of high-frequency electromagnetic waves in medical diagnosis.
  • Make an overhead projector transparency of the spectrum chart on page 24. Ask the students to relate energy to the electro-magnetic wavelengths depicted.

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Last modified prior to September, 2000 by the Windows Team

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