What Is a Wavelength?

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Definition: A wavelength is a term describing how sounds and light waves are measured. The peak of a wave is known as the crest while the low dip of the wave is known as the trough. Wavelength is determined by measuring the distance between each crest.

A Closer Look at Wavelengths

As light and sound travels, they make characteristic wave patterns that include a high point and a low point. Researchers use wavelengths to distinguish between different types of electromagnetic energy.

Visible light, for example, has wavelengths between 400 and 700 nanometers. For comparison, Infrared light has longer wavelengths while Ultraviolet light has shorter wavelengths. Sound wavelengths are much longer than light wavelengths, with most detectable sounds falling somewhere between 5 and 20 centimeters.

Wavelength is generally measured by looking at the distance between crests, but it can also be determined by looking at any similar point between two waves such as the troughs and zero crossings.

While sound and light both travel in waves, they have very different properties.

Wavelength Speed and Diffraction

Light waves travel at a speed about one million times faster than sound waves. Light can travel through a vacuum, however, while sound cannot.  Sound can, however, travel around obstacles and angles, which is why you can often hear things even when they are out of sight. This ability to move around corners is known as diffraction.

Wavelength Absorption and Reflection

Sound wavelengths sometimes bounce off of certain surfaces. This is why you might hear your echo in a cave or the mountains. In other cases, materials can absorb sound wavelengths. Consider the last time you moved into a new house or apartment. At first the empty rooms produced a lot of echoes.

As you added curtains, rugs, and furniture, these surfaces began to absorb the sounds and reduce the echo effect.

Wavelengths and Medium

The wavelength can be affected by the medium that the wave passes through such as air versus water.

Consider this example of the differences between light and sound wavelengths. A researcher places an alarm inside a glass container and removes all of the air. You can still see the alarm even though it now exists in a vacuum, but you are unable to hear it when it goes off.  

So why can't we hear sounds inside of a vacuum? When a sound is produced, it travels through the air by vibrating molecules as it moves along. Sound can only travel through materials such as air, water, and even solid walls. While sounds under water and in a distant room may sound muffled, they are still able to be detected if the originating noise is loud enough.

Since sound waves travel by vibrating molecules, this is also why you can sometimes feel vibrations in your body if the sound is loud enough. When you turn the radio up really loud, you are increasing the amplitude of the sound waves. When the sound waves reach you, they are moving very fast, and their high-energy displaces more molecules around them.

Because of this, you are more likely to feel this energy as it hits your body. Your very sensitive ears, however, are also more likely to suffer damage as a result.