Energy of Waves: Amplitude, Frequency & Energy Loss

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  • 0:00 Energy And Waves
  • 0:40 Energy Content:…
  • 2:30 Energy Loss
  • 3:50 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What gives a wave its energy? In this lesson, we'll learn about amplitude and frequency, and how they relate to wave energy. We'll also learn about how waves lose energy through spreading.

Energy and Waves

If you've ever been in a stadium when they did the wave, you probably saw that waves have a lot of energy! Of course, a physics wave and a stadium wave are not really the same thing. But as it happens it's still true in physics - waves really do have energy.

Waves are vibrations in space and time that carry energy. Since they carry energy, understanding how energy and waves are related to each other is pretty important if you want to understand waves themselves. You really cannot separate energy and waves.

But what is it about waves that determines how much energy they have? Why does one wave have more energy than another? How do you measure this? To find out, let's talk about amplitude and frequency.

Energy Content: Amplitude and Frequency

The amplitude of a wave is how the wave is measured from the rest position or midline to the top of a crest or bottom of a trough, measured in meters. A wave with a large amplitude will be particularly tall, and a wave with a small aptitude will be particularly short.

It turns out that the amplitude tells you how much energy is in the wave. A high amplitude wave is a high-energy wave, and a low-amplitude wave is a low-energy wave. In the case of sound waves, a high amplitude sound will be loud, and a low amplitude sound will be quiet. Or with light waves, a high amplitude beam of light will be bright, and a low amplitude beam of light will be dim.

But amplitude isn't the only factor that affects the energy of a wave. The other factor is frequency. Frequency is the number of ways that pass by each second, measured in hertz. So a wave of a particular amplitude will transmit more energy per second if it has a higher frequency, simply because more waves are passing by in a given period of time.

In fact, in the case of electromagnetic waves like visible light, radio waves, microwaves, infrared, ultraviolet, x-rays, and gamma rays, the frequency and amplitude collectively tell you how much energy is stored inside the wave. For example, light is a wave, but it also contains particles called photons. And each of those photons contains an amount of energy that is proportional to the frequency. So high-frequency light has photons with high energies and appears blue in color.

Thus amplitude and frequency are the two factors that affect the energy transferred by a wave: the height of the wave, and the number of waves passed by each second.

Energy Loss

In physics, we say that energy cannot be created or destroyed, it can only move from one place to another. We call that conservation of energy. So what do we mean when we talk about energy loss?

Well, energy might not be created or destroyed, but it can still move to a place that is less useful for us. When environmentalists talk about saving energy, what they mean is that we need to try to avoid energy transferring to places where we can't use it. In the same way, a wave can lose energy as it travels through a medium, because energy can be absorbed by that medium.

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