Wavelength

Our ears are not sensitive to some of the characteristics that are used to describe sound. One important characteristic that we cannot hear is the wavelength. Since sound travels in a wave, we can relate the words that scientists use to describe sound to a picture of a wave.

a sound wave showing  pressure vs time.

What would a wave look like if you were to make a plot of the pressure in a wave at different positions at a fixed instant in time? It would look exactly the same, except the horizontal axis would be distance instead of time. The following plot is just how a water wave would look if it were frozen at a fixed moment in time.

a sound wave showing pressure vs distance.

If you were to trace your finger across the wave in the diagram above, you would notice that your finger repeats its motion. A wave has a repeating pattern. One such repetition is known as a wave cycle. The length of one wave cycle is the wavelength. The wavelength can be measured as the distance from the top of one wave to the top of the next wave or from the bottom of one wave to the bottom of the next. In fact, the wavelength of a wave can be measured as the distance from a point on a wave to the corresponding point on the next cycle of the wave.

You can also think of the wavelength as the distance that a sound wave travels in one cycle. Wavelength is related to the speed at which sound travels. You can calculate the wavelength of sound in seawater by dividing the speed of sound by the frequency of the sound:

Wavelength = Speed of sound / Frequency of sound

The speed of sound in seawater is the same for all frequencies. A high-frequency sound therefore has a shorter wavelength than a low-frequency sound. Using 1500 meters per second for the approximate speed of sound in seawater we find:

Frequency
(Hertz, or cycles per second)
Wavelength
(meters)
100 15
1000 1.5
10,000 0.15
Additional Resources

  • "Physics Classroom - Properties of Waves." (Link)
  • "Physics Classroom - Sound Properties and Their Perception." (Link)