Question Video: Electromagnetic Waves Used for Communication Physics

Which of the following types of electromagnetic waves is not used for sending communication signals? [A] Infrared waves [B] Microwaves [C] Visible light waves [D] Ultraviolet waves [E] Radio waves


Video Transcript

Which of the following types of electromagnetic waves is not used for sending communication signals? Infrared waves, microwaves, visible-light waves, ultraviolet waves, radio waves.

Okay, so here we want to identify which of these five options is not used for sending communication signals. Now theoretically, any type of wave could be useful in some application for communicating. But in this question, we’re thinking on a practical level, how different kinds of EM waves are actually used currently. We can start at the top of the list and go down, thinking in each case how that particular kind of wave is used or not used in communication.

Starting off with infrared waves, this kind of wave is not typically used to communicate over long distances. But it has been found to be useful for communicating wirelessly over short distances. Think, for example, of any remote controls we might use. When they’re powered on and working properly, when we press a button on the remote, the remote sends an invisible-to-our-eye signal, an infrared signal, to some receiver. We might be sending a signal to power on a monitor, turn off a television, or open our garage door. But regardless of the particular command, we’re sending it using an infrared wave. So there is a communication use for infrared waves, which means we won’t use it as our answer.

Next, let’s consider microwaves. We might first associate these kinds of waves with a microwave oven, something to heat food. Indeed, that’s one of the most common applications of these waves. But it’s not the only thing they’re useful for. Microwaves, when sent from Earth, are very effective and making it through Earth’s atmosphere into space. These waves are unlikely to be blocked or reflected back. For this reason, it’s common to use microwaves to send signals to and receive signals from anything outside of Earth’s atmosphere. Since microwaves do have a communication use, we’ll cross these off our list as well.

Next, let’s consider visible-light waves. Unlike microwaves, visible light is not useful for long-distance communication through the open atmosphere. But with the right constraint, visible light can be useful for sending communication signals. One way this happens is through what is called an optical fiber. An optical fiber is a long wire that has a glass core, a glass interior to it. This interior is covered in a coating. And the way it works is, light is accepted through one end of the fiber and then, regardless of the twists and turns the fiber might go through, that light is safely communicated out the other end. This communication distance from one end of the fiber to the other can be on the order of centimeters or thousands of kilometers. So visible light can be used for long-distance communication so long as it’s traveling through a fiber optic. This means that visible-light signals are useful for communication. So we won’t choose that as our answer either.

Next up is ultraviolet waves. These are waves that in part are absorbed by Earth’s atmosphere. And not only do they have trouble traveling through the atmosphere, but these waves are also invisible to the human eye. So even if we put an ultraviolet signal into one end of an optical fiber, we couldn’t see what would come out the other end. Along with all this, ultraviolet waves are high-energy enough so that some of them are dangerous to humans. They can negatively affect the DNA in our cells and therefore are often avoided. It looks like ultraviolet waves will be the wave type that are not used for sending communication signals.

To make sure this is the case, let’s consider our last option, radio waves. In this case, we can easily think of applications of radio waves for communication. The types of radio stations we’re able to tune into using a radio in our car or in our computer are proof that radio waves are used for communication. So then we can finalize our choice of ultraviolet waves as the type of electromagnetic waves that are not used for sending communication signals.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.