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# Waves Physics

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Waves in Physics are a form of energy transmission. Classically, we see waves as the oscillation caused by energy transmission through a medium. As waves are defined simply as energy transmission in the form of oscillations, there are many different types of waves, such as electromagnetic waves, water waves, or gravitational waves.

## What are progressive and stationary waves?

We can divide waves into stationary waves and progressive waves. Stationary waves do not propagate as they oscillate up and down in the same place. An example of this is the guitar strings when you play the guitar. Progressive waves move from one place to another. A classic example of a progressive wave is an ocean wave.

Figure 1. A progressive wave moves from one place to another. Source: StudySmarter.

Figure 2. A stationary wave does not move from one place to another. Stationary waves are oscillations that appear and disappear in fixed points of space, as shown above. Source: StudySmarter.

### Representing simple waves

To represent simple waves, we use the two simple mathematical functions of sine and cosine, which have cyclical oscillation patterns. You find these in all the mathematics linked to waves.

Figure 3. The sine and cosine functions are used to represent simple waves due to their oscillating behaviour. Source: StudySmarter.

The sine and cosine functions describe certain properties and characteristics that help us to understand waves:

• Amplitude: the height of the wave over the plane of equilibrium. If it is positive, we are dealing with a crest; if negative, we are looking at a trough.
• Crest: the maximum amplitude of the wave from the plane of equilibrium.
• Trough: the maximum negative amplitude measured from the plane of equilibrium.
• Wavelength: the length of a wave from a crest to the next crest, which is denoted by the symbol ‘λ’ and measured in metres.
• Wave height: denoted by the symbol ‘H’ and measured in metres, the wave height ‘H’ is the vertical distance between the crest and trough.
• Period: the time it takes for a wave to repeat its oscillation pattern, which is denoted by the symbol ‘T’ and measured in seconds.
• Frequency: the number of times a wave repeats during a time interval equal to a second, which is denoted by the symbol ‘f’ and measured in hertz.
• Wave speed: the velocity at which a wave moves, which is denoted by the symbol ‘c’ and measured in m/s.

Figure 4. Two very important parameters of a wave are its height (H) and wavelength (λ), both of which depend on its dimensions. Source: StudySmarter.

### Examples of waves in nature

As waves represent a form of energy transmission, you can find them everywhere: in solid materials, in fluids, in the air, or in the vacuum of space. See the following examples of waves:

• Wind waves: the waves you see on the beach or in the ocean are created by the wind blowing over the ocean’s surface.
• Sound waves: vibrations that are the product of mechanical waves moving through air. The source of vibrations is an object moving at high speed, such as a guitar string.
• Radio waves: electromagnetic waves that are the product of charges oscillating rapidly.
• Seismic waves (earthquakes): occurring in solids, these are mechanical waves that are the product of the moving of tectonic plates.
• Vibration waves: produced by the movement of a material, these are similar to seismic waves and also move in solids.
• Gravitational waves: the product of masses oscillating in space, these propagate in the fabric of space.

### Waves that transport mass

When waves are progressive in nature, they move from one place to another, as in the case of sea waves. However, in addition to this, sea waves also carry water with them. Progressive waves can also occur in the atmosphere.

### Transport of energy in waves

Progressive waves, therefore, can transfer not only mass but also energy. To be precise, they transport kinetic energy as they move across the medium, causing it to vibrate up and down. Examples of this are ocean, sound, and seismic waves. The energy transfer, which is parallel to the movement of the wave, is easily seen as waves move from one place to another.

### Mechanical waves in solids

Waves can also appear in solid materials, in which case they act as seismic waves. These waves only transport energy within the material. If, for instance, you knock over a table, you can feel the vibrations inside the table with your hands. These vibrations are seismic waves propagating through its body.

## Waves Physics - Key takeaways

• Waves are oscillations that transport energy in space.
• Waves can be present in many energy exchanging phenomena, such as electromagnetic waves (light), ocean waves, sound waves, seismic waves, and atmospheric and any mechanical/energy vibrations.
• Waves have several important parameters, such as their height, length, frequency, period, and velocity.
• Waves can be progressive or stationary.
• Progressive waves move from one point to another, while stationary waves only appear and disappear at fixed points in space.

A sound wave is a progressive mechanical wave in the air. Sound waves are longitudinal waves, as the oscillation is parallel to the direction of the movement.

A longitudinal wave is a wave whose direction of oscillation is parallel to its direction of propagation. Seismic waves are an example of longitudinal waves, as are the pressure changes in the air caused by sound waves.

A transverse wave is a wave whose oscillation is perpendicular to its propagation. An example of this is water waves whose up and down movements are perpendicular to their horizontal movement.

A wave is an energy transfer process in space and time. The movement of energy changes some of the properties of the space in which it moves. An example is sound waves, where the wave movement compresses and expands the air molecules as it passes.

To calculate a wave’s frequency, you need to find a fixed point in space and then measure the time it takes for two consecutive crests to pass that point. The time it takes for a wave to repeat its oscillation pattern is known as its period. To obtain the wave’s frequency, you need to take the inverse of this period, as shown in the formula below:

f=1/T

In this formula, ‘f’ is the frequency, while T is the period in seconds.

## Final Waves Physics Quiz

Question

What are waves?

A form of energy transmission consisting of oscillations.

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Name the two types of waves as defined by their movement.

Stationary waves and progressive waves.

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What is a stationary wave?

A wave that does not move in space but only appears and disappears at fixed points in space.

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What is a progressive wave?

A wave that moves in space from one place to another.

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List the most important parameters of a wave.

Wave height, wave amplitude, wavelength, wave period, wave frequency, and wave speed.

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What is a wave’s height?

The distance between a wave’s crest and its trough.

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What is a wave’s amplitude?

The height of a wave over the plane of equilibrium, such as the surface of the sea.

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What do we mean by wavelength?

The distance that covers an entire wave cycle, such as the distance from one crest to another.

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What is a wave’s period?

The time it takes for a wave to repeat its oscillation pattern.

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What is a wave’s frequency?

The number of times a wave repeats during a time interval equal to a second.

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Do progressive waves transport energy?

Yes, they do transport energy.

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Can progressive waves transport mass?

Yes, they can transport mass.

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Is sound a wave?

Yes, sound is a mechanical wave.

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Which functions do we use to represent waves in maths?

Sine and cosine.

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What is the amplitude of a wave with a height of 2m?

1 metre.

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What is a progressive wave?.

A wave that moves from one place to another in space.

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What is a stationary wave?.

A wave that does not move in space but appears and disappears as fixed oscillations in space.

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What type of waves are ocean waves?.

Progressive waves.

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What type of waves are the vibrations of a string between two fixed points?.

Stationary waves.

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Do waves propagate in solids, liquids, or gases?.

They propagate in all three.

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Can waves propagate in a vacuum?.

Yes, they can.

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Waves can carry mass, but can they also carry energy?.

Yes, they can also carry energy.

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Name an example of waves that carry both energy and mass.

Ocean waves.

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What is a node?.

A fixed point in a stationary wave that does not change or move.

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What is a harmonic?.

A multiple of the original frequency.

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Are seismic waves progressive waves?.

Yes, they are.

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Are mechanical waves occurring in a solid progressive waves?.

Yes, they are.

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Do nodes in stationary waves move?.

No, they don’t.

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If you have a string vibrating within a fixed length of space and there are two nodes between the two fixed extremes, which harmonic do you have?.

3rd harmonic.

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If you have a string vibrating within a fixed length of space and there are three nodes between the two fixed extremes, which harmonic do you have?.

4th harmonic.

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S waves transfer energy in a direction perpendicular to their movement.

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The displacement of transverse waves can happen in many possible directions.

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Longitudinal waves usually appear on material media.

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The wavelength is related to the energy of the wave.

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Transverse waves and longitudinal waves propagate through time and space.

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What is a wave?

A wave is a disturbance that propagates through time and space.

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What is the amplitude of a wave?

The amplitude of a wave is the length of the displacement caused by the wave.

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Do all waves have a period?

No, only periodic ones do.

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Is sound made of longitudinal or transverse waves?

Sound waves are longitudinal.

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Are the waves generated in an earthquake longitudinal or transverse?

Both types, P waves are longitudinal, but S waves and surface waves are transverse.

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Are all waves purely transverse or purely longitudinal?

No, most waves have displacements in both directions.

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Can you name an everyday example of a longitudinal wave?

The movement of a spring when stretched or compressed.

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Is the frequency of a wave related to its energy?

Yes, the frequency carries information on how much displacement the wave can generate per unit of time.

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Is the amplitude of a wave related to its energy?

Yes, it is. A larger amplitude corresponds to a greater displacement, which, in turn, corresponds to a larger transfer of energy.

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Longitudinal waves do not have a wavelength. True or false?

False. If a periodic motion happens, it can be characterised by a wavelength independently of the type of displacement involved.

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Transverse waves transfer their energy towards the direction in which they are moving. True or false?

False. Transverse waves transfer their energy towards a direction that is perpendicular to the direction of their movement.

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Only transverse waves have a polarisation.

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All transverse waves can be polarised.

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There are many types of polarisation, such as linear, circular, elliptical ….

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Polarised lenses dim light coming from different sources, but not totally.

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