Wavelength Definition: Lesson for Kids

Instructor: Josh Corbat

Josh has taught Earth Science and Physical Science at the High School level and holds a Master of Education degree from UNC-Chapel Hill.

Waves are all around us. You've probably seen waves in an ocean or lake, but sound and light also travel as waves. In this lesson, we'll take a look at waves and how they are measured. We will focus on one measurement in particular: wavelength.

Waves in Our Daily Lives

Have you ever gone swimming in an ocean or big lake? As you splash around in the water, you may have noticed that the waves were crashing over you in a pretty regular pattern. What makes this happen? As you dive into and under the waves, what makes them roll toward shore at a certain speed and spaced either far apart or close together? This all has to do with the energy in the water. Waves look and act differently based on the amount of energy in them. Measuring waves is basically measuring their energy. One such measurement, wavelength, is related how far apart each wave is.

What is Wavelength?

Imagine yourself back in the ocean or lake. Think about how far apart each wave crest is. The crest is the highest point of the wave. If you're floating on the crest of one wave and can see the crest of another, you are looking at the wavelength of that wave! Wavelength is the measured distance between two identical points on two back-to-back waves. Thinking back to our ocean example, to measure the wavelength we would measure the distance between two back-to-back crests, or we could measure the distance between two troughs, which are the lowest part of a wave.

The distance between two crests or troughs is the wavelength of the wave.
Wavelength

Waves are Everywhere!

Waves are not just found in water. Sound and light also travel through the air as waves. Measuring these waves helps us understand more about them. For example, the longer the wavelength of a sound wave is, the lower the pitch of the sound. In other words, it will sound lower, like playing a key on the left side of a piano or plucking a thick string on a guitar. The wavelength of a light wave determines its color. That's right: If the wavelength of a light wave changes, you will see it as a totally different color!

Waves can either have long or short wavelengths. The wavelength can change how we perceive the wave.
Long and short waves

Measure it Yourself!

Want to try and measure the wavelength of a wave yourself? All you need is:

  • a measuring device (like a meter stick or tape measure)
  • a piece of string or a Slinky
  • a device that takes pictures (This can be done without the device, but it's way easier to take a picture and look at the wave without it moving.)

Here's what you do:

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