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.
