When we hear the word wave, many things can come to our heads. Maybe we picture someone waving their hand at us to say hello, perhaps a stadium wave, or we might think of water moving across the ocean to touch our feet on the beach. In physics, a wave is a very specific phenomenon, but there are multiple examples, and they all have the same wave characteristics, even if they do not seem related at first glance! Did you know that sound is a wave that makes our eardrums vibrate to hear? Light is a wave, too; it bounces from objects and reaches our eyes so we can see. Waves are everywhere! This article will give you a better understanding of what waves are, review their characteristics, and discuss some interesting examples.
Wave Characteristics
Before we jump into the characteristics of waves, we need to know what we call a wave in physics.
A wave is a form of energy traveling progressively from point to point in a medium.
You should always remember that a wave conveys energy from one place to another, but it does not transport matter, even if it seems so.
Fig 1 - The waves crashing across the ocean is an example of wave motion
Properties of a Wave
Waves have the following properties:
- As a wave travels in a medium, the particles of the medium are not displaced from one place to another. They only vibrate along their equilibrium positions.
- Each particle in the medium shows a similar motion to the prior particle.
- During wave motion, only energy is transferred.
Waves come in two kinds – longitudinal and transverse.
Longitudinal Waves
Let's check out what exactly longitudinal waves are.
Longitudinal or compression waves are those in which a quantity oscillates in the same direction of the wave's motion.
The quantity that oscillates in a wave could be, for example, pressure, electric or magnetic fields, etc.
Longitudinal waves are often produced when particles vibrate in a medium. A sound wave is a perfect example of a longitudinal wave! The propagation speed of sound waves depends upon the composition and the temperature of the medium.
Transverse Waves
Now, let's see what transverse waves are.
Transverse waves are those in which a quantity oscillates perpendicularly to the direction of the wave's motion.
The ripples on the surface of the water, the secondary waves of an earthquake, and electromagnetic waves, such as light, are all examples of transverse waves.
Waves have three main characteristics: wavelength, amplitude, and time period. Let's get a better knowledge of each one of them.
Wavelength Characteristics of Waves
We will now dig deeper into the wavelength characteristics of a wave.
The wavelength is the distance between two equivalent points in a wave.
Usually, in transverse waves, the wavelength is measured between two crests or two troughs, and likewise, in longitudinal waves, it is measured between two successive compressions or rarefactions.
Fig 2 - The wavelength characteristics of a wave defining two consecutive crests or troughs.
Compression is a region in the longitudinal wave where the particles are the closest together, whereas we call it a rarefaction if the particles are at their farthest.
Wavelength is usually given by the Greek letter lambda, \( \lambda \). We can calculate the wavelength if we know the velocity and frequency of the wave using the following equation
\[ \lambda = \frac{v}{f},\]where \(\lambda\) is measured in meters \( \mathrm{(m)}\), velocity, \(v\), in meters per second \( \mathrm{(m/s)} \), and frequency, \(f\), in inverse of seconds \( \mathrm{(s^{-1})}\), commonly referred to as hertz \( \mathrm{Hz} \).
Wave speed, \(v\), is defined as the distance covered by a wave in a given period, whereas frequency, \(f\), describes the number of waves that pass a fixed place in that amount of time.
For light, wavelength is used to determine its color. The wavelength of the visible light ranges from about \( 650\;\mathrm{nm} \) to \( 400\;\mathrm{nm} \), which we perceived as red and violet, respectively. On the other hand, the wavelength of a sound wave determines its pitch.
Amplitude Characteristics of Waves
Let's discuss what exactly the amplitude of a wave is and go through some examples.
The equation for the displacement of a wave with respect to its equilibrium position depends of the amplitude of the wave.
\[y=Asin(\omega * t + \Phi)\]
In the above equation \(y\) is the displacement of the wave in meters \( \mathrm{(m)} \), \(A\) is the amplitude of the wave in meters \(\mathrm{(m)} \), \(\omega\) is the angular frequency of the wave given in \(\frac{\mathrm{rad}}{s}\), \( t \) is the time period in seconds \(\mathrm{(s)} \), and \(\Phi\) is a constant called the phase difference.
The phase difference is the path difference between the two waves.
Displacement is a vector quantity defined as the change in position of a particle. In the next section, we will learn more in detail about the period of a wave.
Ripple sound of water produced in lakes
When you observe someone throwing a stone into a water body, you can hear some sound and observe a circular pattern that forms around the point of impact. Both of these are waves! We measure the amplitude of the water wave from the higher point of the wave to the water level. In the case of the sound wave, we say that a low sound has a small amplitude, whereas a loud sound has a high amplitude.
Listening to headphones
When we listen to some music with our headphones, we constantly increase or decrease the volume. When we change the volume, it means we are changing the amplitude of the wave resulting in high or low sound.
Time-Period Characteristics of Waves
The last wave characteristic to review is the period of a wave.
The period is the time a wave takes to complete a cycle or full oscillation.
The period should not be confused with the frequency, even though they are closely related. The period is defined as a time interval that responds to the question of how long an event takes. While the frequency refers to how frequently an event happens and responds to the question of how many times an event occurs in a specific amount of time.
Think of a woodpecker making a hole across the brunch of the tree. If the woodpecker impacts the tree twice in one second, we say the frequency is \(2\;\mathrm{Hz} \). Each time it hits the tree, it must endure for one-half a second, so the period is \(0.5\;\mathrm{s} \). If the woodpecker does so six times in one second, then the frequency is \(6\;\mathrm{Hz} \); each time, it must endure for one-sixth of a second, so the period is \(0.17\;\mathrm{s} \). Finally, if the woodpecker pecks on a tree ten times in one second, the frequency is \(10\;\mathrm{Hz} \); it endures for one-tenth of a second, so the period is \(0.1\;\mathrm{s} \). Do you realize the distinction?
Mathematically, the period is the inverse of the frequency, and this is can be expressed as follows:
\[ t = \frac{1}{f}, \]where the period, \(T,\) is measured in seconds\( \mathrm{(s)} \), and the frequency, \( f, \) is measured in inverse of second \( \mathrm{(s^{-1})} \), or hertz \( \mathrm{(Hz)} \).
Examples of Wave Characteristics
We will now discuss some examples of waves and talk about their characteristics.
Light waves
Visible light, like any other wave, is a form of energy propagating from a source. It is an electromagnetic wave comprised of an oscillating electric and magnetic field.
When the light comes from the source, our brain depicts the waves interpreting the different wavelengths as different colors.
The energy of a wave is directly proportional to its frequency, or equivalently, it is inversely proportional to wavelength. The range of the visible wavelengths to the human eye is from \( 400\;\mathrm{nm}\), which we interpret as violet, to \(700\;\mathrm{nm} \), which know as red. Based on their wavelengths, we can conclude that red light carries less energy than violet light. It is also interesting to note that electromagnetic waves do not need a medium to propagate; they can exist in vacuum!
Fig 3 - Light waves transmitting energy to our brain while it depicts different colors assigned to different wavelengths
Sound waves
Sound waves are made up of alternating compression and rarefaction patterns. When a sound wave travels in a medium, the wave's energy causes the molecules to be excited. So, when a wave passes, a molecule gets excited or energized in the medium until it gives its energy to the following molecule and diminishes its motion. Then, the prior will again acquire the power until it is hit by some molecule in the wave, resulting in alternate compression and rarefaction.
Sound waves lose energy as they travel in a medium. This is why we can't hear a person standing too far away from us compared to someone next to us. In the case of sound waves, the energy is proportional to the amplitude of the wave, which defines its volume. And the period or frequency defines the pitch of the sound.
Fig 4 - Headphones use energy to create sound waves. Increasing the volume increases the amplitude of the waves and requires more energy.
Microwaves
Microwaves fall under electromagnetic radiation. They have ample applications, starting in communications, radar, and even in households like cooking.
Microwaves are used in small devices for signal processing, in radar guns and motion detectors to detect speed, and even in weather radars to track the motion of water droplets in the atmosphere. Microwaves are also used in satellites to look back at the Earth or space.
Another use you might be familiar with is to heat food quickly or cook. Microwave ovens work emitting these types of waves causing the food molecules to vibrate, increasing their energy and temperature. Because they are electromagnetic waves just like light, they propagate at the same speed and their energy depends on their frequency.
Fig 5 - A microwave oven heats food by emitting waves that cause the food molecules to vibrate, increasing their energy and temperature
Wave Characteristics - Key takeaways
A wave is a propagating disturbance that conveys energy.
Longitudinal and transverse are the two main types of waves: some propagate along and the others perpendicular to their wave motion.
Wavelength is the distance between two equivalent points in a wave.
Amplitude is the maximum displacement or distance moved by a point on a wave measured from its equilibrium position.
The period of a wave is defined as the time a particle in a medium takes to make one complete cycle.
Sound, visible light, and microwaves are all examples of waves. The wave characteristic determines different properties in each of these cases, for example, in sound, amplitude determines the volume and frequency determines the pitch. In light, wavelength determines the color we perceive and also its energy.
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