Figure 1 shows an incomplete list of the parts of the electromagnetic spectrum. What name is given to the type of waves that would belong to the position labelled A in Figure 1? Tick one box: Ultraviolet, Visible Light, Microwave.
Looking at Figure 1, we see it’s a representation of the electromagnetic spectrum. It shows us different types of waves in that spectrum, including radio waves, infrared radiation, and X-rays. We see though that along with the given wave types, we have some unknown or mystery wave types marked out as A, B, C, and D. We don’t know what each one of these wave types is. But we do know that they’re in their proper position on the spectrum.
The spectrum that we see in Figure 1 is organized. It ranks different types of electromagnetic radiation according to their energy and wavelength. For example, if we start at the left end of our spectrum, where we have radio waves, we know that the energy of radio waves is very low while the wavelength of radio waves is very high, sometimes on the order of kilometers long. Then, as we move the other direction along the spectrum, these properties change. So that by the time we get all the way up to the right end, we have very high energy waves that have a very short or low wavelength.
This progression from high to low energy and from low to high wavelength will be helpful to us when we’re trying to figure out what type of radiation is labelled A in this figure. Basically, we’re looking for a type of radiation that has less energy and longer wavelength than infrared radiation and somewhat more energy and shorter wavelength than radio waves.
Recall that our choice options are ultraviolet light, visible light and microwave radiation. We can consider these options starting from the top. Ultraviolet light is higher energy than infrared light. It’s this type of radiation which is known to give us sun tans and then, if we’re out for too long, sunburns. Infrared radiation, on the other hand, is not high energy enough to cause these effects. So we know that our first option, ultraviolet light, is somewhere to the right of infrared on our spectrum. It has more energy and a shorter wavelength. So that means ultraviolet light is not a candidate for the type of waves that would belong in the position labelled A.
So then, what about visible radiation? This sketch shows our eye and different colors of light our eye is sensitive to. There is blue light, green light, yellow light, and red light. Now the question is: Does this visible light appear to the right of infrared radiation in Figure 1 or to the left? In other words, is it higher energy or lower energy than infrared radiation? There’s a useful clue to what the answer is, simply in the name infrared.
The word infrared means below red. So infrared radiation occurs in this direction on the spectrum from visible light. That is, it has a lower energy or a longer wavelength. So if infrared radiation is lower energy than visible light radiation, that means that visible light appears somewhere to the right of infrared in Figure 1. That is, it’s not a candidate for the waves labelled A. This leaves us with our last option, microwaves.
And microwaves indeed do fit between radio waves and infrared radiation. They have a shorter wavelength than radio waves, that is are higher energy. But they have a longer wavelength than infrared radiation, that is a lower energy. And as we know, they’re also great waves for heating up food. That’s the box we tick indicating that the waves labelled A in Figure 1 are in fact microwaves. Let’s move on to look at some applications of various types of waves on the spectrum.
Different parts of the electromagnetic spectrum can be applied to different uses. Draw one line from each type of electromagnetic wave to an application of that type of wave.
In the left column, we see the types of waves we want to match with applications, which are listed in the right-hand column. For each wave type, we want to draw just one line to an application. In other words, each wave will match with one application. Let’s start with radio waves. And we’ll consider which of these four applications best applies to radio waves.
We said earlier that radio waves are fairly low energy compared to other types of waves on the electromagnetic spectrum. So low energy, in fact, that even if we were to stand all day being bombarded by radio waves, which in fact we are, there wouldn’t be enough energy involved to give us a tan to our skin. A different type of radiation with more energy than radio waves is needed for that. So then, what about radiotherapy? It seems like there might be a match here just because of this word radio that appears in both terms. But once again, this application requires more energy than radio waves are able to supply.
We move on then to the application of tracking aircraft. Now, this is actually something that is a good fit for this type of wave. Radio waves are very adept at moving through long distances of atmosphere without being significantly disturbed. So when they run into a solid object and are reflected back towards their source, that strong reflection is a reliable sign that some large moving object, such as an aircraft, has been encountered. Thanks to their long wavelength, radio waves are well-suited to this application. All this, by the way, helped to give rise to the term radar, which stands for radio detection and ranging. So we found then an application for radio waves; it’s to track aircraft.
Next, what about X-rays? Which of the remaining applications fits that type of wave? We’ve now moved near to the other end of the electromagnetic spectrum for radio waves. And we’re working with a very high energy, very short wavelength type of radiation. Thanks to this high energy, X-rays, we know, are used in medical applications. For example, for taking X-rays of potentially broken bones and also for irradiating potentially dangerous cells in our body.
This is the idea behind radiotherapy. Say that there are cells in a person’s body that begin to multiply in an out-of-control way. When this happens, this uncontrolled growth is known as a cancer and is very dangerous to our bodies. In radiotherapy, powerful X-rays are directed right at these out-of-control cells. The energy supplied by the X-rays is enough to damage the DNA of these cells so they’re no longer able to reproduce. In this application then, the strong power of X-ray radiation is directed at destroying something that we want out of the body. That’s an application for X-rays.
Finally, what about infrared radiation? What’s an application of that? Our options, we see, are getting a sun tan and finding people buried under debris. We saw earlier that infrared radiation is lower energy than visible light radiation. As a result, we’re not able to use infrared light to get a sun tan. If infrared light were shined on our skin, we would feel warm. But that’s about it.
Now interestingly, not only can we feel infrared light but our bodies also produce it themselves. Maybe you’ve seen one of those kinds of creepy-looking pictures of a person shown in infrared light. When we look at a person through this type of light, then cold spots on their body appear dark and warm spots appear bright. The point is, thanks to the fact that we emit infrared radiation ourselves. That means that our bodies create a signal that could be detected by an infrared radiation detector.
Now this can be quite useful because sometimes people are being searched for in rescue situations. For example, a person lost at sea or someone buried under a pile of rubble. Infrared radiation, and specifically detectors that are able to sense infrared radiation, are commonly used in search and rescue scenarios. So an application of infrared is finding people buried under debris. Since we just wanted to draw one line from each type of radiation to an application, we’re now done with this part of the question. Next, let’s consider how different types of radiation affect the human body.
From the type of electromagnetic waves from the box, select the type that cannot be harmful to people.
Of these three types of radiation, we want to figure out which of them cannot be harmful to people. What we’re going to look for here is a type of radiation which is very unlikely to be harmful to people. Because really under some creative unusual circumstance, all of these types could possibly be harmful to a person. We could think of this then as which of these types of radiation is least likely to be harmful to people.
We can begin considering our options starting at the highest energy end of this list. X-rays, we know, certainly can be harmful to people. Say, for example, that during an accident, you hurt your arm and you wonder if it’s broken. So you go to the doctor’s office and have an X-ray image created of the bone in your arm. Before the X-ray is administered though, you’re probably be given a large very heavy weight covering to put on the rest of your body. This covering, which is often made of lead, is designed to block any stray X-rays that might reach the rest of your body when your arm is being imaged. So the simple fact that we need to wear protection is an indication that X-rays can indeed be harmful to people.
But what about infrared radiation? Is that likely to harm people? Typically, infrared light is not harmful to us. It’s what’s called nonionizing radiation. And as we mentioned earlier, our bodies emit infrared radiation. So that might make us think that it can’t be harmful to us. And yet, it’s possible to concentrate infrared rays to such a high intensity that those rays do become harmful to people.
An example of this is an infrared laser, such as this carbon dioxide laser shown here. Even when this laser is in operation, we’re not able to see its beam because the light is invisible to our eyes. But it’s there, nonetheless, and can be quite powerful. If we were to look directly into this laser light, never recommended, then our eye wouldn’t see any light because it’s invisible. But we would potentially suffer damage over time, sometimes a very short period of time. Not only that, light from this laser can be damaging to skin and other tissues. So infrared radiation, like X-rays, very much has the capacity to be harmful to people.
This leaves us with the least energetic of the waves listed here, radio waves. Radio waves are around us all the time in the atmosphere. These types of waves, being the least energetic of the three types listed here, have the smallest capacity for harm to people. It’s still possible for harm to occur but much less likely with waves of this type.