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# Properties of Waves Save Print Edit
Properties of Waves
• Astrophysics • Atoms and Radioactivity • Electricity • Energy Physics • Engineering Physics • Fields in Physics • Force • Further Mechanics and Thermal Physics • Magnetism • Measurements • Mechanics and Materials • Medical Physics • Nuclear Physics • Particle Model of Matter • Physical Quantities and Units • Physics of Motion • Radiation • Space Physics • Turning Points in Physics • Waves Physics If you're a bit confused about different types of waves and the various words used to describe them then you have come to the right place! Waves are a type of energy pathway and are one of the ways how energy can be transferred between energy stores. They do not transport matter, only energy. A wave is essentially an oscillation or a vibration about the rest position, transmitted through a medium or a vacuum. Scientists can define the nature and behaviour of these waves using wave property terms, such as amplitude, frequency, period, and wavelength. This article will help you understand the science behind all of these terms.

## Different types of waves

Waves can be either transverse or longitudinal. The difference depends on the direction of the wave's oscillations. If the oscillations of the wave are perpendicular (right angle) to the direction of travel then the wave is transverse. However, if the oscillations are parallel (same direction) to the wave's direction of travel then the wave is longitudinal. Comparison between a transverse wave and a longitudinal wave, Wikimedia Commons CC BY 4.0

One example of a transverse wave is the electromagnetic wave, where both the electric and magnetic components of the wave oscillate perpendicular to the direction of travel. Another example can be seen in the diagram above, where a woman is generating a transverse wave in a slinky by vibrating the first coil up and down in the vertical direction. Sound waves are a typical example of a longitudinal wave, where the particles vibrate back and forth parallel to the wave's direction of travel.

Another important distinction when discussing waves is whether a wave is mechanical or non-mechanical. The main difference between these two types of waves is if the wave requires a medium to travel through or not. Light can travel through the vacuum of space, which means they are non-mechanical waves: they do not need a medium to travel. All electromagnetic waves are different types of light, encompassing the entire electromagnetic spectrum from radio waves to visible light to gamma rays. Meanwhile, mechanical waves require a medium to travel through. The medium could be any solid, liquid, or gas, such as iron, water, or air.

## Wave frequency

The wave frequency is defined as the number of full waves passing an arbitrary point in space every second. The wave period is the time taken for just one full wave to pass a point.

Waves with shorter periods will have higher frequencies, as more waves can pass through a point every second. On the other hand, waves with a longer period would have lower frequencies, because fewer waves can pass through a point every second. Comparison of high frequency and low frequency waves, highlighting the wave period, adapted from image by Wikimedia Commons

Below is a formula used to calculate the frequency and the period of a wave ,

where is the frequency of the wave and is the period of the wave In words, the equation above reads .

Question 1

A wave has a period of . What is the wave's frequency?

Use the formula relating wave frequency and period .

Question 2

If full waves of a wave pass an arbitrary point in space in one second, how long is the period of this wave?

If full waves per second pass a point, we have a wave frequency of . Rearrange the formula given earlier to make the period the subject .

## Wave amplitude

Below you can see a simple diagram of a wave. It has several labels that help us identify wave characteristics with wave terms.

The wave crest (or peak) is the highest point of oscillation above the rest position, while the trough is the lowest point of oscillation below the rest position.

The amplitude of a wave is the maximum displacement between the rest position and its crest.

Alternatively, you could measure the maximum displacement between the rest position and the trough as well to get the amplitude of the wave. Diagram showing wave properties relating to amplitude, Wikimedia Commons CC BY 3.0

The wave amplitude can help inform us about how much energy is in a wave. For example, big (tall) water waves carry more energy than little waves, as you might have experienced yourself. Another example is that an electromagnetic (light) wave with a high amplitude will be brighter than a dimmer, low amplitude wave. Similarly, a sound wave with a high amplitude will be louder than a wave with a lower amplitude.

Question 3

The vertical displacement between the crest and trough of a water wave is . What is the wave's amplitude?

Wave amplitude is only measured between the crest and the rest position, or the trough and the rest position. The crest and trough of the wave have an equal displacement from the rest position. Therefore, you can divide the displacement between the crest and the trough by to calculate the amplitude of the wave, which is .

## What is wavelength

You can also observe that one full wavelength is the length of one complete cycle of the wave, most easily measured either crest-to-crest or trough-to-trough. Both wave amplitude and wavelength are measured in units of distance, with the standard unit as metres.

Question 4

The distance between two consecutive wave crests is . What is the total length of wavelengths?

The distance between two consecutive wave crests is equal to one wavelength. The length of wavelengths means you must multiply this number by , so the answer to the question is .

The total vertical displacement between the crest and the trough of a wave is actually a wave property known as wave height , which we measure in . Wave height is a particularly useful concept in coastal science. It is equal to twice the wave amplitude , .

## Wave speed and phase

This section will help you to understand the slightly more complex concepts of wave speed, phase, and interference. Other wave properties previously discussed within this article (wave amplitude, wavelength, frequency, and wavelength) should all be understood before continuing.

### Wave Speed

A very useful equation to know when solving wave problems is the wave speed equation. This equation is used to calculate the speed that a wave is travelling at, using the product of the wave's frequency and its wavelength ,

where is the wave speed , is the frequency , and is the wavelength . In words, this equation is .

The speed of a wave is constant if the medium the wave travels through is also constant. For instance, the speed of sound in air with a temperature of at sea level is approximately . Using the wave equation, we can see that increasing the frequency of a wave will decrease its wavelength proportionally. The opposite is also true! By decreasing the frequency of a wave then its wavelength will increase proportionally. This means the only way to change the speed of a wave, is to change the medium it travels through! Summarising, we have .

Consider a sound wave travelling from air into the water. The sound waves that aren't reflected at the water's surface will become heavily distorted. The speed of sound in water is approximately , a factor of about greater than in air. This is partially due to the increased density of the water medium compared to air. The sound waves can travel faster in a denser medium as it is easier for particles to bump into each other when oscillating/vibrating.

Question 5

A wave has a frequency of and a wavelength of . What is the wave speed?

Convert into standard units, which reads , then use the wave speed equation to determine the wave speed as follows: .

We conclude that the wave speed is .

Question 6

A wave propagates through a medium with a wavelength of . In the same medium, what would the wavelength be if a new wave had double its frequency?

The speed of a wave is constant in the same medium, . If you double the frequency of a wave then you must halve its wavelength for the speed to remain constant, as follows: .

Therefore, the new wavelength would be , or .

### Wave phase and interference

More than one wave can occupy the same position in space at the same time. If two waves coincide when their peaks and troughs match completely, then they are in phase with each other. This is called constructive interference. The two waves superimpose on each other, increasing the total wave amplitude. However, if two waves coincide where the peaks of one wave meet the troughs of another wave, then they are considered to be out of phase. The waves destructively interfere with each other, resulting in zero amplitude. Comparison of waves out of phase and wave in phase, where the composite wave is shown in the upper part of the diagrams, Wikimedia Commons CC BY-SA 3.0

## Properties of Waves - Key takeaways

• Waves act as an energy pathway, which is a way to transfer energy between energy stores.
• A wave is a vibration/oscillation about the rest position, transmitted through a medium or a vacuum.
• If the wave's oscillations are perpendicular to the direction of travel then they are transverse waves. However, if the wave's oscillations are parallel to the direction of travel then they are longitudinal waves.
• Mechanical waves require a medium to travel through, while non-mechanical waves can travel through a vacuum, like electromagnetic (light) waves.
• Wave frequency is the number of full waves that pass an arbitrary point every second.
• Wave period is the time for exactly one full wave to pass a point.
• Wave amplitude is the displacement between the crest (or trough) and the rest position.
• Wavelength is the length of one complete wave, typically measured crest-to-crest.
• The wave speed equation is , and the wave speed is constant in the same medium.
• When two waves superimpose in phase with each other it causes constructive interference, two waves out of phase will create destructive interference.

The wave amplitude is the maximum displacement between the rest position and the wave's crest (or trough). Wave amplitude can help inform us of how much energy is in a wave.

Imagine an electromagnetic (light) wave. An EM wave with a very high frequency would have many full waves passing an arbitrary point per second. It would be either an x-ray or gamma-ray and it acts differently to a low-frequency wave, such as an infrared or radio wave.

A wave period is the time taken for just one full wave to pass a point in space. Waves with shorter periods will have higher frequencies, as more waves can pass through a point every second.

One full wavelength is the length of one complete cycle of the wave, typically measured crest-to-crest. It is measured in units of distance or metres.

Wave speed is simply the speed a wave crest is travelling at. It can be calculated using the product of the wave's frequency and wavelength.

The phase of two waves describes the offset between two waves occupying the same point in space. In-phase waves have peaks and troughs that align completely and constructively interfere. Out-of-phase waves have the peaks of one wave meet the troughs of the second wave, causing destructive interference.

Electromagnetic waves are transverse waves, where the electric and magnetic components of the wave oscillate perpendicular (at a right angle) to its direction of travel. Electromagnetic waves are light waves.

Longitudinal waves oscillate parallel (same direction) as the wave's direction of travel

## Final Properties of Waves Quiz

Question

Electromagnetic waves consist of what two types of fields oscillating at right-angles to each other?

Electric and Magnetic fields.

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Question

Are electromagnetic waves transverse or longitudinal waves?

Electromagnetic waves are transverse waves.

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Question

'Ultraviolet radiation has a higher frequency than infrared radiation '. Is this statement true or false?

This statement is true. Ultraviolet light has a higher frequency and therefore higher energy than infrared radiation which has a longer wavelength than ultraviolet light.

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Question

What effect could cause a change in the movement of the charges in the coil, creating a current?

Charges placed in an electric field are subjected to a force, and if they are able to move, they will.

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Question

Can a magnetic field be created by the presence of an electric field?

Changing electric fields produce magnetic fields and changing magnetic fields produce electric fields.

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Question

Define an 'EM' wave.

Electromagnetic waves, often known as EM waves, are waves that are formed when an electric field and a magnetic field oscillate at right-angles to each other. EM waves can be thought of as disturbances in the electromagnetic field.

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Question

'The electric and magnetic components of an EM are perpendicular to each other'. Is this statement true or false?

An electromagnetic wave is a transverse wave in which the electric and magnetic fields oscillate in perpendicular directions to one another and to the wave's propagation direction in all cases.

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Question

What do electromagnetic waves carry from one location to another?

Electromagnetic waves, like other waves, transport energy from one location to another.

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Question

How are electromagnetic waves different from all other waves?

Electromagnetic waves are distinct from mechanical waves in that they do not propagate via a medium. They can propagate through empty space.

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Question

Name one application of microwaves

Microwaves are used in telecommunication because they can penetrate clouds, smoke, and light rain.

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Question

What type of electromagnetic wave is used in TV remote controls?

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Question

Which type of electromagnetic radiation is radiated by the Sun and causes sunburns?

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Question

How many different types of EM waves exist?

There are seven main types of electromagnetic waves: Radio waves, microwaves, infrared radiation, visible light, ultraviolet light, x-rays and gamma radiation.

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Question

Can waves transport matter, energy or both?

Energy

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Question

Name 3 wave properties

Any 3 of the following:

• Wave frequency
• Wavelength
• Wave amplitude
• Period
• Wave speed
• Wave phase
• Wave height

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Question

Can mechanical waves travel through a vacuum?

No.

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Question

Which type of wave has oscillations act perpendicular to the direction of travel of the wave?

Transverse.

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Question

What wave property is defined as the number of full wave cycles that pass through a point every second?

Frequency.

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Question

Will waves with greater time periods have higher frequencies or lower frequencies?

Lower.

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Question

What is one way to measure the amplitude of a wave?

From the wave crest to the rest position.

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Question

How would you define wavelength?

One wavelength is the length of one complete wave cycle, typically measured from crest-to-crest or trough-to-trough. It is measured in units of distance or metres.

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Question

Wave A is identical to wave B, except wave A has double the amplitude. Which wave has more energy?

Wave A.

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Question

What happens to the speed of a wave if the medium it travels through does not change?

It stays the same

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Question

What type of interference occurs when 2 waves that are in phase superimpose on each other?

Constructive Interference

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Question

2 waves destructively interfere with each other. Are they in phase or out of phase?

Out of Phase

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Question

What are the units for wave speed?

meters per second (m/s)

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Question

All of the different electromagnetic waves are referred to as:

The electromagnetic spectrum.

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Question

Can we see x-rays?

No, we can only see a small part of the electromagnetic spectrum called visible light.

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Question

The maximum displacement of a point on a wave from its undisturbed position is called:

The amplitude of the wave.

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Question

What is the wavelength of a wave?

The distance  from a peak to a trough.

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Question

The time it takes for two consecutive peaks, is known as:

The period of the wave.

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Question

Do all the waves in the electromagnetic spectrum travel at the same speed?

Yes, all the electromagnetic waves are the same physical phenomena.

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Question

Electromagnetic waves transport ...

Energy. This is why microwaves can make the food temperature increase.

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Question

Imagine that you are in room surrounded by objects that can only reflect electromagnetic waves. The light of the room has been replaced by a special bulb that only emits ultraviolet. What would happen?

We would not see anything, because the objects would reflect ultraviolet radiation which we cannot see.

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Question

Which of the following statements about the electromagnetic spectrum is true?

All electromagnetic waves from the spectrum can propagate in vacuum.

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Question

Is the energy of an electromagnetic wave increases as...

Its frequency increases.

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Question

Which category of waves in the electromagnetic spectrum are the most harmful because of their high frequency and energy?

Gamma rays.

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Question

Which of the following category of electromagnetic waves is less energetic?

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Question

Consider electromagnetic waves in the same medium.  As the frequency of the waves increase, their wavelength...

Decreases.

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Question

Radio waves and the light we see are both electromagnetic waves.

Yes, they are both example of the same physical phenomena. This is why both propagate at the same speed.

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Question

In the visible light spectrum, what differentiates each colour of light from the next?

Each colour differs by its frequency or wavelength.

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Question

Which of the following options talking about sound are correct?

Sound is a wave.

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Question

What happens when a source exceeds the wave speed of the waves it generates?

The waves are left behind and the wavefronts accumulate forming a shockwave.

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Question

Have a look at the following options. Which ones are correct?

A wave is a propagating disturbance or oscillation of one or more physical quantities.

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Question

A man is floating in a swimming pool thanks to a lifesaver. A small kid jumps into the pool, at a right angle to the water surface, forming waves in the water. However, the man is not displaced away from the kid. Why?

Because the waves do not exert a force on the water outwards. The water just moves up and down with respect to the water level.

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Question

The speed of sound in water is greater than its speed in air. Therefore, as a sound wave changes from air to water ...

Its wavelength increases.

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Question

While observing distant stars, some astronomers say 'light is our connection with the past.' What do you think this means?

The light of stars takes a certain amount of time to reach us. Therefore, the image we see is not what the start looks like at the moment we receive its light but what it looked like when this light was emitted.

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Question

Which of the following waves can propagate in a vacuum?

Light.

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Question

Two waves with the same frequency are emitted from a source. The first one has a wavelength of two metres and the second has a wavelength of three metres. Both waves travel 100 metres to where a receptor is waiting. Which wave takes less time to reach the receptor?

The second wave.

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Question

What is the boundary between two media called?

Interface

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