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5.26: Wave Amplitude

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On a windy day, moving air particles strike these flags and transfer their energy of motion to particles of fabric. The energy travels through the fabric in waves. You can see the waves rippling through the brightly colored cloth. The windier the day is, the more vigorously the flags wave.

What’s the Matter?

Waves that travel through matter—such as the fabric of a flag—are called mechanical waves. The matter they travel through is called the medium. When the energy of a wave passes through the medium, particles of the medium move. The more energy the wave has, the farther the particles of the medium move. The distance the particles move is measured by the wave’s amplitude.

What Is Wave Amplitude?

Wave amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. The resting position of a particle of the medium is where the particle would be in the absence of a wave. The Figure below show the amplitudes of two different types of waves: transverse and longitudinal waves.

  • In a transverse wave, particles of the medium move up and down at right angles to the direction of the wave. Wave amplitude of a transverse wave is the difference in height between the crest and the resting position. The crest is the highest point particles of the medium reach. The higher the crests are, the greater the amplitude of the wave.
  • In a longitudinal wave, particles of the medium move back and forth in the same direction as the wave. Wave amplitude of a longitudinal wave is the distance between particles of the medium where it is compressed by the wave. The closer together the particles are, the greater the amplitude of the wave.

You can simulate waves with different amplitudes in the animation at this URL: http://sci-culture.com/advancedpoll/GCSE/sine%20wave%20simulator.html

Q: What do you think determines a wave’s amplitude?

A: Wave amplitude is determined by the energy of the disturbance that causes the wave.

Energy and Amplitude

A wave caused by a disturbance with more energy has greater amplitude. Imagine dropping a small pebble into a pond of still water. Tiny ripples will move out from the disturbance in concentric circles. The ripples are low-amplitude waves with very little energy. Now imagine throwing a big boulder into the pond. Very large waves will be generated by the disturbance. These waves are high-amplitude waves and have a great deal of energy.

Summary

  • Wave amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through.
  • Wave amplitude of a transverse wave is the difference in height between a crest and the resting position. Wave amplitude of a longitudinal wave is the distance between particles of the medium where it is compressed by the wave.
  • Wave amplitude is determined by the energy of the disturbance that causes the wave. A wave caused by a disturbance with more energy has greater amplitude.

Vocabulary

  • wave amplitude : Maximum distance the particles of a medium move from their resting positions when a wave passes through.

Practice

Read about wave amplitude at the following URL. Examine the graphs and answer the two questions. Click on the links to see if your answers are correct. http://cse.ssl.berkeley.edu/light/measure_amp.html#measure4

Review

  1. Define wave amplitude.
  2. What is the amplitude of the transverse wave modeled in the Figure below if the height of a crest is 3 cm above the resting position of the medium?

  3. Which of these two longitudinal waves has greater amplitude? (See Figure below )

  4. Relate wave amplitude to wave energy.

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Description

Difficulty Level:

Basic

Grades:

7 , 8

Date Created:

Nov 01, 2012

Last Modified:

Aug 08, 2014
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