Video: Applications of Electromagnetic Waves

In this lesson, we will learn how to describe the uses of different types of electromagnetic radiation in a variety of applications and technologies.

13:22

Video Transcript

In this video, we’re talking about applications of electromagnetic waves. In our everyday life, there are already dozens of places where electromagnetic waves play apart. Any time we turn on a television, send or receive a text, or heat up some food in a microwave, we’re using electromagnetic waves. In this lesson, we’ll talk about some of the leading applications and the kinds of waves they correspond to.

To get started, one of the first points we can make about electromagnetic waves, sometimes called EM waves for short, is that they carry energy. This means that as an electromagnetic wave travels along, it transmits energy from one spot to another. The amount of energy a particular wave transmits has to do with its wavelength, the distance from one peak of the wave to an adjacent peak, or equivalently from one trough to the next trough over. The wavelength, this straight-line distance between peaks or troughs, can be longer as it is for this wave, or shorter as it is for this one. The shorter the wavelength, the more energy a wave has. So, this wave in pink, because it has a shorter wavelength, has more energy than the wave in blue.

Now, when it comes to the wavelength of electromagnetic waves, there’s no particular upper or lower limit. A wave’s length could be as short or as long as we could imagine. If we were to organize all electromagnetic waves by their wavelength, then we would have what’s called a spectrum of waves. In particular, we would have what’s called the EM, or electromagnetic, spectrum. This spectrum can be organized visually by putting waves with a shorter wavelength toward one end, in this case we’re putting them towards the left end of our spectrum, and waves with a longer wavelength are towards the other end, in this case towards the right.

To further organize the electromagnetic spectrum, it’s been useful to divide it up into seven regions. These regions include visible light, the light our eyes are sensitive to, then to the right of that at longer wavelength is infrared radiation, abbreviated IR. Then, to the right of that come microwaves. And then finally, radio waves, those waves with the longest wavelength of any on the spectrum.

If we go back to visible light and move the opposite direction on the spectrum towards shorter wavelengths, we encounter the UV or ultraviolet region. Then, we get into the X-ray portion of the spectrum. And finally, there are gamma rays, those waves with the shortest wavelengths of all. Notice that even though the spectrum is divided up at the ends, at the far left and at the far right, there’s no end point. This is due to what we noticed earlier, that there was no lower or upper limit to the wavelength an EM wave can have.

Now that we have all these regions arranged by wavelength, let’s recall that energy goes down as wavelength goes up. That is, as we get towards the radio wave end of our spectrum, where the wavelength is very long, the energy in those waves is very low. And then, the opposite happens as we move towards the other end, towards gamma rays. Headed in his direction, our wavelengths are getting shorter and shorter, and the wave energy is going higher and higher. The applications for which these various parts of the spectrum are most useful have to do with how much energy those waves carry. Let’s start by considering the least energetic waves, radio waves, and consider what they may be useful for.

Let’s say that this is the Earth. This is Earth atmosphere, and we want to communicate from one spot on Earth surface to another that’s out of line of sight from the first location. In other words, we want to communicate from here to here. But if we try to send a straight-line signal, it will run into the earth. This is where radio waves can come in very useful. When these waves travel through the atmosphere, they’re capable of bouncing off of atmospheric layers and back to Earth. This enables sending radio signals by reflection, like we see here.

Or using other radio waves, it’s possible to create a wave that bends inside Earth atmosphere. This is called refraction. Whether through reflection or refraction, it’s possible to use radio waves to accomplish long-distance, wireless communication. This application of radio waves has become so common that the devices we typically use to receive these waves are called radios.

Now, if we then shift over to the microwave region of the spectrum, we once more encounter a category of wave with an application that’s so common it’s named after the wave. We’re talking here about microwaves, as in microwave ovens. When we put food in such an oven, it’s indeed exposed to microwave radiation. The wavelength of this radiation is a wonderful match for exciting water molecules, heating them up. And since water is in virtually all the food we eat, heating up the water in food effectively heats the food. For this to work, the incoming microwaves need to be absorbed by the food. That’s how energy is transmitted into it. Though there are definitely other applications for microwave radiation, this one, heating food, is one of the most common ones.

When we go from the microwave to the infrared region of the spectrum, the light we’re considering is still invisible to our eye. We’re not able to see it, but nevertheless it has some very real physical effects. For example, imagine standing near a campfire in order to warm up. Now, we know that light from the campfire, visible light, is available to our eyes, but there is another type of radiation responsible for the warm feeling of the campfire on our hands. That’s infrared radiation, IR. The warming effects of the campfire and many other heat sources are due to these invisible electromagnetic waves.

This, for example, is how radiators in many homes work. If we’d look at a radiator while it’s in action, we can see it’s not emitting any visible light, but it is giving off heat. And the way it does that is through infrared radiation. By the way, along with warming objects, there is another common application for infrared radiation. Whenever we use a remote control to do something like turn on or off a television, we’re using infrared radiation. The signal that sent from the remote is infrared, invisible to our eyes, but very real nonetheless.

Now, when we move on to the visible portion of the spectrum, arguably, this is the portion where there are the most applications for this kind of light. This is because visible light by its nature is so useful to us. So, of the many applications of visible light we could pick, here is one. It’s possible to take visible light in one location, say over here, and reproduce it in another, say over here, using a device called an optical fiber.

If we were to look closely at one end of this fiber, we would see that the core of it, the center, is made of glass and the glass is covered in a coating. This glass core is what serves as a channel, a conduit, for the visible light from one place to another. The fiber is designed so that no matter how it bends or twists between these two locations, the light is faithfully reproduced at the other end. This transmission of visible light can happen over distances of thousands of kilometers. And because this communication happens with visible light, the images that go into and come out of the fiber or collection of fibers can be seen by our eye. Fiber-optic signaling is a long-distance communication application for visible light.

Moving on to ultraviolet radiation or UV for short, we now cross back over into invisible light, light our eyes can’t see. Now, ultraviolet radiation is often thought of as hazardous. And here is the reason why. We can see that as we move from right to left in the ultraviolet region of the spectrum, the energy of these rays gets higher and higher. Now, if we think about these increasingly energetic waves interacting with an atom, here is an atom with its nucleus and then the surrounding electrons, as the incoming radiation shown here gets higher and higher in energy, it becomes more and more capable of ionizing this atom.

In other words, when this ray is absorbed by an electron in the atom, that electron takes on the energy of the wave and now has so much energy that it leaves the atom entirely. And after it’s gone, what’s left over is a charged atom, an ion. The point at which incoming radiation becomes energetic enough to strip an electron away from an atom is considered significant. If the wave can strip an electron away, it’s called ionizing radiation because it’s capable of creating an ion. But if it’s not energetic enough, it’s called nonionizing. And the boundary between ionizing and nonionizing radiation falls in the ultraviolet portion of the spectrum.

So, some ultraviolet radiation with wavelengths in this region is incapable of stripping electrons away from atoms and therefore is nonionizing. But some UV rays in this region here are high-energy enough to do this. An ionizing radiation is considered hazardous because of the damage it can do to human cells. This is why, for example, the use of sunscreen is encouraged whenever people are outside in direct sunlight for long periods of time. It’s to shield our skin from the ionizing radiation given off by the sun. As we’ll see later, ionizing radiation can actually be useful for health applications. But it’s not directly related to the particular ultraviolet application we’ll name.

At one time or another, many of us have had the experience of being in a room where the only light supplied was coming from what was called a black light. Typically, black lights don’t actually look black, but have a violet or a purple hue to them. That’s because they occupy roughly this portion of the EM spectrum. Some of the light they give off is low-energy, visible light. That’s in the violet end of that spectrum. But most of it is low-energy, nonionizing ultraviolet radiation.

Now, in the presence of a black light, any clothing that’s white in color takes on a very interesting appearance. It looks like it’s glowing. This effect is due to what’s called fluorescence. Fluorescence is a two-part process that has to do with ultraviolet radiation shining on something, that object absorbing the radiation and then being energized itself, starting to emit light, typically, of a lower wavelength than the UV light that reached it. Our eyes aren’t able to see the ultraviolet light that energizes the objects that end up fluorescent, but we often can see the vibrant colors that are given off by these energized objects.

Fluorescence is often used to create lighting in office buildings. Overhead lights that look like long tubes have ultraviolet radiation inside them that reaches the inner surface of these tubes. These surfaces are coated in a phosphor which gives off visible light when energized by ultraviolet light. Ultraviolet radiation is absorbed by the material in the tube while visible light is given off to the outside.

As we move on to the X-ray portion of the EM spectrum, we see that the wavelength of our waves is increasingly getting shorter while the energy is going up. X-rays are energetic enough that they’re capable of penetrating through different kinds of matter. For example, if we send a lot of X-rays into our hand, then only the bones in the hand are dense enough to absorb and block the X-rays. The X-rays that don’t hit bone are able to pass right through. This, of course, makes X-rays useful for medical imaging.

But they’re useful in other ways as well, say, at the security checkpoint at an airport. Here, X-rays are commonly used to see into the interiors, the insides, of boxes and suitcases. Once again, the very high energy of these waves means they’re only capable of being blocked by something fairly dense. They can travel right through the outside of luggage. Whether used for health or safety or something else, imaging the interior of different objects is an important application of X-rays.

Last but not least, let’s consider an application of gamma rays, the highest-energy radiation on the EM spectrum. All gamma rays are ionizing, meaning they’re all capable of stripping an electron away from an atom and creating a charged particle. As such, gamma rays are capable of doing a lot of damage to human cells. At first, this might not sound like a good thing, but we can keep in mind that not all cells are good cells. When cells in our body mutate to become something they shouldn’t and then start to rapidly divide, this can be the beginning of the development of a cancerous tumor.

Before the tumor continues to grow for much longer, we’d like to destroy it by destroying the cells it’s made up of. This is where an application of gamma radiation comes in. Because these waves are so high energy, when they interact with a cell, a typical response is for the cell to die. In this case, with the cells dividing in an out-of-control way, that’s a good thing. Through careful application, gamma ray therapy is capable of destroying a cancerous tumor. In this way, the ionizing property of gamma rays have been put to useful application.

As we step back and consider these different applications for different kinds of electromagnetic waves, it’s worth reminding ourselves that this is just a small sampling of the long list of ways that EM waves are used. That said, let’s summarize what we’ve learned about the applications of electromagnetic waves. Starting off, we saw that electromagnetic waves, called EM waves for short, carry energy from one place to another. We also learned that wave energy is inversely proportional to wavelength. That is, as the wavelength of a wave increases, its energy decreases and vice versa. We saw that the EM spectrum is commonly divided into seven regions and that each one of these seven regions has an application it’s known for.

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