Applications of Waves

Applications of wave motion

Water waves seem the most obvious and easily identifiable type of waves. The motion of the waves is periodic and sometimes tranquil but in the case of a tsunami, those waves can become destructive. One of the simplest applications of waves requires making use of the energy carried by water waves as they move. Tidal power is the power generated by the velocity of the flow of seawater. Tidal power stations are built in the ocean to capture tides as they move in and out. The kinetic energy of water can be used to generate electrical energy. The amount of energy currently generated by tidal power is not significant but it can be done, which in itself is remarkable.

Applications of sound waves

Sound waves can be generated in gases, like air, but also liquids and solids. Sound waves are longitudinal waves, meaning the air particles vibrate in the same direction in which the wave is propagating.

Applications of sound waves: The Ear

The most common and probably most important use of sound waves is in everyday verbal communication. When we speak, the movement of the various parts of our mouth causes vibrations in the air surrounding it. These vibrations are carried through the air by disturbing neighbouring air molecules. This propagating chain of disturbances continues until the sound wave reaches its intended target, which is usually the ear of the person we are speaking to. Sound waves consist of areas in which air molecules are squashed closer together; these are called compressions. Areas in which the air molecules are further apart are called rarefactions. The figure below shows areas of compression and rarefaction in a typical sound wave.

A sound wave moving from source to ear. Dark areas have more vibrating air molecules (compressions) whereas lighter areas have fewer (rarefactions), Wikimedia Commons CC 1.0

The frequency limits of the human hearing range are$20\mathrm{Hz}$to$20\mathrm{kHz}$. Any sound with a frequency below$20\mathrm{Hz}$or greater than$20\mathrm{kHz}$cannot be detected by a human. This frequency range is known as the audible spectrum.

Applications of sound waves: Sonar

Sound waves can be used for communication, music and other applications that rely on sound travelling through air. Sound can also travel through liquids and solids. Sound travels faster through water than it does through air, and also travels greater distances in water than in air. This fact is one of the factors that gave rise to the concept of sonar. Sonar is an acronym that stands for 'sound navigation and ranging'. It is the use of sound waves in water to detect underwater obstacles, such as sea mines, and objects that are hidden beneath the surface of the ocean, for example, submarines.

Sound waves which travel through water undergo an important property of wave motion when they encounter an obstacle; reflection. A source of sound or ender emits a sound wave that travels outward, hits an object, is then reflected and returns toward the sender. A receiver is then used to detect the reflected wave (echo) and compare it to the profile of the original wave to ensure the reflection truly is the same wave. The distance$r$to the object can then be determined since the speed of the wave in water is known. The wave travels a total distance of$2r$in the round trip to the object and back in a time$t$. Since the speed of sound in water$v$is constant, the distance$r$can be found as follows by

$\begin{array}{lcl}\mathit{2}r& =& vt\\ \mathit{}r& =& \frac{vt}{\mathit{2}}\end{array}$

The principle behind the operation of sonar can be viewed from the diagram below. The original wave strikes the obstruction, which is the object. It then reflects toward the sender and is eventually received.

The principle behind the operation of sonar. A wave is emitted by a sender and received after being reflected by the object. The time taken for the wave to return indicates the distance of the object, Wikimedia Commons CC BY-SA 3.0

Applications of sound waves: Ultrasound

If you have ever seen a scan of a baby in a pregnant woman, you would have seen an image that shows the features of the foetus. This is an example of the use of ultrasound waves in medicine. Ultrasound waves use a similar principle to that of sonar; reflection. A device called a transducer is used to generate and receive sound waves that have a frequency hundreds of times greater than the upper limit of human hearing. The sound waves are partially reflected at the boundaries of different tissues in the human body. Reflected waves are received by the transducer which transforms this into a digital signal that is viewed as the image. The various tissues and body structures reflect the waves in different directions and with different amplitudes. The result is an image of the structure of interest (tissue, organ, etc.) that is produced. The image below is an example of an image produced by ultrasound.

An ultrasound image of the inferior vena cava in a human. An ultrasound pulse is sent into the body and the variations in the intensity of the reflected pulse are used to create this image.

Ultrasound waves of lower frequencies can penetrate to a greater depth in tissue but the detail in the resultant image is lower. Higher frequency ultrasound waves cannot penetrate as deep but provide an image with a greater resolution. We can determine the depth of the boundary between tissues beneath the skin surface, using the equation that we did for sonar, i.e.,

$r=\frac{vt}{2}$

where$v$is the speed of the ultrasound wave,$t$is the total time taken for the wave to be emitted and received by the transducer and$r$the depth of the tissue boundary.

Applications of radio waves

Radio waves are the electromagnetic waves in the electromagnetic spectrum with the longest wavelengths of approximately$1\mathrm{km}$. They can, hence, travel the longest distances of all electromagnetic waves. Due to this ability to travel long distances, radio waves are typically used for communication and detection. We will discuss two applications of radio waves, that are, mobile phones and radar. Radio waves contribute to background radiation and are generally considered safe, however, it is best practice to stay far from the source of radio waves. The international hazard symbol of harmful radio waves is shown in the figure below.

The image shows the hazard symbol for radio waves. It generally means that you are close to a source radio waves and should remain clear of the area, Public Domain Vectors

Applications of radio waves: Mobile phones

Not only do radio waves travel long distances, but they are also good at penetrating solid materials, such as walls. This makes the radio wave ideal for carrying cellular and telephone signals. Cellular phones have built-in receivers and transmitters. Transmitters work by converting audio signals into electromagnetic radio waves. The radio waves then travel long distances and are routed and relayed via cellular stations and towers until it reaches the phone of the recipient. The receiver then decodes the signal back into audio, which is played back to the recipient. Another advantage of radio waves in this application is that they travel at the speed of electromagnetic waves in free space, which is$c$;$300$million metres per second! This means that communication can happen almost instantaneously with very little delay. The figure below shows a picture of a typical cell tower.

This image is of a typical cell tower that is used to relay radio waves from sender to receiver. The towers are usually tall to ensure that most of the waves are not absorbed by the ground.

Applications of radio waves: Radar

Radar is an acronym that stands for radio detection and ranging. The principle behind Radar is quite similar to sonar, but electromagnetic waves are used rather than sound waves. Sound waves don't travel significantly fast enough in air to be useful in detecting obstacles, e.g., an incoming aircraft. We, therefore, turn to waves in the electromagnetic spectrum which can also undergo the wave motion property of reflection to detect objects that are in the sky. Radio waves are transmitted through the air via large antennas, reflect when they strike an obstacle and return via the same medium to the receiver. We can then use the time it takes for the radio wave to return to determine the distance to the object. The wave travels a total distance of$2r$in the round trip to the object and back in a time$t$. Since the speed of electromagnetic waves$c$in air is constant, the distance$r$can be found as follows by

$$\begin{gathered} \mathit{2}r\mathit{=}ct \\ \mathit{}\mathit{}r\mathit{=}\frac{\mathit{c}\mathit{t}}{\mathit{2}} \end{gathered}$$

The image below shows a picture of a radar antenna that can send out electromagnetic radio waves and receive the reflected waves as well. The size of the radar is proportional to the distance over which signals can be sent or received.

An image of a radar antenna that is capable of sending out a radio wave and receiving the reflected wave. The antenna is relatively large in size to ensure that signals can be sent and received over long distances.

Application of light waves

Recall that light waves are electromagnetic waves, like radio waves, that lie in the visible region of the electromagnetic spectrum. Simply put, light is an electromagnetic wave that we can see. You may not think that there are many applications of light waves but that is probably because we have become accustomed to always having our surroundings illuminated. Spend a night without electricity and the importance of light suddenly becomes more apparent.

Applications of light waves: Flash photography

Have you ever noticed a professional photographer's bag? It is quite large in comparison to the size of the camera. One of the most important pieces of equipment, that can sometimes be larger than the camera itself, is the flash. A camera flash is a device that supplies a short, intense beam of light to illuminate the scene for a photograph to be taken. The white light produced is intense enough to brighten an image and allow for a clearer picture of higher quality to be taken. This is a simple but common example of the application of light waves. The figure below is that of a typical camera flash.

This image shows a bright white flash that is generated by a modern digital camera. The flash is used to illuminate the scene for a photographer allowing for a clearer image to be taken, Wikimedia Commons