What is Wave Absorption? - Definition & Examples

Instructor: Damien Howard

Damien has a master's degree in physics and has taught physics lab to college students.

When a wave contacts matter, there are several different interactions that can occur. One of those interactions is wave absorption. In this lesson we'll learn what it means for a wave to be absorbed, and look at a couple examples of the effects of wave absorption.

Waves and Matter

We live in a world that is always being bombarded by waves. Water waves crash upon the shore. Electromagnetic waves in the form of visible, ultraviolet, and infrared light constantly bathe the Earth in their radiation. Even the sounds you hear consist of waves originating from something else and hitting your eardrum. Waves are always colliding with the matter in the world around us.

So, what happens when a wave runs into matter? Three of the most prominent outcomes of waves colliding with matter are that they can be transmitted, reflected, or absorbed. A transmitted wave passes through the matter, like sound coming through the wall from the room next to you. A reflected wave bounces off the surface it hits, like light reflecting off a mirror. Finally, an absorbed wave transfers its energy to the material it penetrates.

Wave Reflection Transmission and Absorption
wave matter interactions

While you can quickly come up with easily relatable examples of waves being transmitted and reflected, what exactly does it mean for a wave to transfer its energy through absorption? In this lesson, we're going to learn what happens to a wave during absorption and what happens to the material that absorbs it.


To understand how waves are absorbed, we need to talk about what they're interacting with in the absorbing material. At the most basic level, every material can be broken down into individual atoms and molecules. It's these atoms and molecules that the wave is transferring its energy to during absorption.

Once the wave's energy has been transferred to a material's atoms and molecules, they start vibrating. This vibration then releases the transferred energy in the form of heat. Have you ever been to the beach when the sand is too hot to stand on with bare feet? The heat being given off by the sand is the product of the electromagnetic waves from the sun that the beach has been absorbing.

Wave Absorption Process Diagram
wave absorption process diagram

Finally, we should note that a wave can either be completely or partially absorbed. A completely absorbed wave transfers all its energy to the atoms and molecules of the absorbing material and fully disperses. A partially absorbed or attenuated wave only transfers some of its energy to those atoms and molecules. It then transmits through the absorbing material with a lower energy level than before the wave entered the material.

Absorption Effects

As we said at the start of this lesson, waves are surrounding us all the time, and as such, waves are also constantly being absorbed all around us. We've already seen that the main effect of waves being absorbed is the conversion of the wave's energy into heat, but there are also other effects of wave absorption we can observe.

For one, every object's color is determined by the combination of wave absorption and wave reflection. The colors we see are the wavelengths of visible light that are reflected off an object, and the colors we don't see are the wavelengths that are absorbed by it. So, a healthy blade of grass absorbs all colors of visible light except green, and then reflects the green color of light back to our eyes. Objects that are pure white like snow are reflecting all visible light, and objects that are pitch black like asphalt absorb all wavelengths of visible light.

Green Object Reflection and Absorption of Visible Light
green object reflection and absorption

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