Wave Motion

Wave Motion refers to the transfer of energy and momentum from one point to another in a medium without actually transporting matter between the two points. Wave motion is a kind of disturbance from place to place. Wave can travel in solid medium, liquid medium, gas medium, and in a vacuum. Sound waves, light waves, ocean waves, seismic waves, and microwaves are examples of wave motion.

Through this article, we will learn more about wave motion, types of waves, wave motion characteristics, and some important terms related to wave motion.

What is Wave Motion?

Wave motion is a mode of transfer of energy, pressure, and momentum from one point to another point of the medium without the actual transport of matter between two points.

Sound waves, light waves, seismic waves, and ocean waves are examples of wave motion. Wave can travel in medium and in a vacuum too. Wave motion travels in all three mediums that are solid, liquid, and gas. There are different types of wave motion present in physics such as electromagnetic waves, matter waves, mechanical waves, etc.

Wave Motion Definition

Wave motion is the transfer of the energy and momentum traveled from one point to another point in a vacuum or medium (solid, liquid or gas) without changing the matter’s property by a motion.

Classification of Wave Motion

Waves can be classified in various waves based on different parameters. The main classification parameters are described below:

• Classification Based on Medium of Propagation
• Classification based on the Motion of Wave in a Space
• Classification Based on Transfer of Energy

Classification Based on Motion of Wave in Space

The waves are classified into three types based on the motion of wave in a space. They are as follows:

• One-Dimensional waves
• Two-Dimensional waves
• Three-Dimensional waves

Wave Type	Definition	Example
One-Dimensional waves	The wave that moves along one dimension only is called a one-dimensional wave.	Waves produced in a string.
Two-Dimensional waves	The wave that moves in a plane is called a two-dimensional wave.	Ripple in water.
Three-Dimensional waves	The wave that moves in a three-dimensional space is called a three-dimensional wave.	Propagation of light and sound waves.

Classification Based on Medium of Propagation

Waves are classified into three types based on the requirement of medium. They are as follows :

• Mechanical waves
• Electromagnetic waves
• Matter waves.

Mechanical Waves

Mechanical wave is a disturbance in matter that transfers energy through the material medium (solid, liquid or gas). Mechanical waves can not propagate in vacuum. Mechanical waves can travel in air, water and solid Earth. Mechanical waves are classified into three types which are:

• Longitudinal waves
• Transverse waves and
• Surface waves.

Mechanical waves carry or transport energy like the all other waves. The direction of energy propagation and mechanical waves propagation is in the same direction.

Electromagnetic/Non-mechanical waves

Electromagnetic waves or non-mechanical waves are the waves that do not require any medium for their propagation. Electromagnetic waves are produced when electrically charged particles accelerate and interact with other particles.

In an electromagnetic wave, the electric field and magnetic field come to contact perpendicularly (at right angles) to each other. The direction of Electromagnetic waves are perpendicular to the direction of the electric field and magnetic field.

Electromagnetic waves are further classified into the following:

• Radio Waves
• Microwaves
• Infrared Waves
• Visible Light
• Ultraviolet Waves
• X-rays
• Gamma Rays

Learn more about, Electromagnetic Waves

Matter Waves

According to De-Broglie, matter waves are the waves which is associated with each moving particle. According to this concept, when matter particles are in motion at higher velocities, they exhibit wave-like behavior. The associated wavelength of these matter waves is known as the De Broglie wavelength and is defined by the equation:

λ = h / p

Where:

• h is Planck’s constant (6.62 × 10^-34 m² kg/s),
• p is the momentum of the particle,
• m is the mass of the particle, and
• v is the velocity of the particle.

Classification Based on Transfer of Energy

Depending upon the transfer of energy, waves are classified into two types. These are –

• Progressive waves
• Stationary waves

Progressive Wave

Progressive Wave travels continuously in a certain direction in a medium. Progressive wave is also known as travelling wave. In an infinite or unbounded medium, the progressive wave travels in a particular direction transferring energy and momentum between the particles of that medium.

Stationary Waves or Standing Waves

Stationary waves are produced when two similar waves having same amplitudes and same wavelengths traveling in the same straight line, but in opposite directions and collides each other. They appear stationary, with nodes (points of zero amplitude) and antinodes (points of maximum amplitude).

Types of Wave

Apart from other discussed classification of waves, some other types of wave are illustrated in the table below:

Wave Type	Definition	Example
Periodic Wave	Periodic Wave waves repeat their pattern of oscillation regularly over time.	Sine waves and Square waves.
Non-periodic Wave	Non-periodic Wave does not repeat their pattern of oscillation regularly over time.	Transient signals and Noise.
Transverse Wave	In transverse waves, the particles of the medium oscillate perpendicular to the direction of wave propagation	Light waves and waves on a string.
Longitudinal Wave	In longitudinal waves, the particles of the medium oscillate parallel to the direction of wave propagation.	Sound waves and Seismic waves.
Surface Wave	Surface Waves travel along the boundary between two different media.	Surface of water wave.
Body Wave	Body waves propagate through the interior of a medium.	Sound waves traveling through air.
Continous Wave	Continous waves have a continuous range of frequencies or wavelengths and are characterized by a smooth, uninterrupted oscillation pattern.	Sine waves and Cosine waves.
Discrete Wave	Discrete waves have distinct, separated frequencies or wavelengths. They are characterized by a discontinuous or discrete set of oscillation	Pulse waves.
Linear Wave	Linear waves follow the principle of superposition, where the combined effect of multiple waves is the algebraic sum of their individual effects	Light Waves in a Homogeneous Medium.
Non-linear Wave	Non-linear waves that do not obey the principle of superposition and can exhibit complex behaviours.	Shock Waves.

Wave Motion Characteristics

The main characteristics of the wave motion is as follows:

• In a medium, the particles vibrate their mean positions. The particles of the medium do not move.
• It travels at the same speed in all directions in a medium.
• The speed of a wave motion depends upon the nature of the medium through which it moves.
• Energy, pressure and momentum etc. are transferred from one point of the medium to another point. During this transfer, there is no move of the matter.

Few other Characterstics of wave motion are explained below:

• Amplitude
• Period
• Wavelength
• Frequency
• Wave velocity

Amplitude (A)

The amplitude of a wave is the maximum displacement of any particle of the medium from its original or mean position. For describing the size of wave, amplitude is used. It is denoted by letter A and it’s SI unit is metre (m).

Period (T)

The period of a wave is the time taken by two consecutive rarefactions or compressions to a fixed point or in other word, any particle of the medium to complete one vibration or oscillation during a period (T). Time period is denoted by letter T and it’s SI unit is Second (S). Time period is inversely proportional to frequency.

Time period = 1/Frequency

Wavelength (λ)

Wavelength is the length between two consecutive compressions or rarefactions. Wavelength is denoted by lambda and it’s SI unit is metre (m).

Frequency (f)

Frequency is the number of vibrations made per second by any particles of the medium (f = 1/T). The frequency of a wave does not change with change in medium. It’s SI unit is hertz ( Hz).

Wave Velocity (v)

Distance travelled per second by a wave is called wave velocity. It defines the speed of the wave. It is denoted by letter v. It’s SI unit is metre per second (m/s or ms^-1).

Important Terms Related to Wave Motion

The following important terms are related to wave motion. These terms are

• Reflection
• Refraction
• Intensity
• Angular Frequency
• Polarization
• Time Difference
• Phase Difference
• Path Difference

Below is the explanation of each terminology:

Reflection

Reflection is an important property of wave motion that is displayed by visible light. Reflection arises when the light which is travelling through a specific medium is incident onto a boundary between two media, and the light ‘bounces’ off the boundary or changes direction upon striking this boundary and moves on in the initial medium.

Read More, Reflection of Wave

Refraction

Refraction is an another important property of wave motion that is exhibited by visible light. It comes when light rays move from one medium to another medium and for this, it changes direction and speed. Refraction can be happened in sound waves, water waves and other waves along with light waves.

It can be possible for us to have lenses, magnifying glasses, prisms and rainbows by the bending property of refraction. Even our eyes depend upon the bending property of refraction of light. We couldn’t be able to focus light onto our retina without refraction of light.

Read More About, Refraction of Light

Doppler Effect

Doppler effect is identified as the motion-related frequency change. It is applicable for both sound waves and electromagnetic waves. Doppler effect is the fluctuation in the intensity of sound because of distance. The decrease in the sound of the loudspeaker when a person moves away and the sound gradual increase when the person comes near, is an example of the doppler effect.

Intensity

Intensity of wave is the energy carried by a wave per unit time across a unit area surface. The SI unit of Intensity is watts per square meter (W/m²). The intensity of a wave is the property that is proportional to the square of its amplitude.

For example, the intensity of an electromagnetic wave is proportional to the square of the wave’s electric field amplitude.

Read More, Intensity

Polarization

Polarization refers to the orientation of the oscillations of a wave in a particular direction. It is a phenomenon that occurs primarily in transverse waves, such as electromagnetic waves (e.g., light waves) and some mechanical waves (e.g., waves on a string). The best well known example of polarization is Linear and circulation polarization.

Read More About, Polarization

Interference

Interference is a phenomenon that occurs when two or more waves meet at the same point in space and time. It results from the superposition of wave patterns, where the waves combine to form a resultant wave. Interference is two types – constructive and destructive interference.

Angular Frequency

Angular Frequency is the rate at which the change in rotation takes place or the rate at which change in the sinusoidal waves occurs. In other words, we can define, Angular Frequency is the angular displacement of an element of a wave per unit time.

The SI unit of angular frequency in radian per second and the equation of angular frequency can be written as,

ω =2πf

Where,

ω = angular Frequency and

f = frequency

Time Difference (ΔT)

Time difference means the time taken to travel from one point to another by the wave through the medium.

Phase Difference (ΔΦ)

Phase difference means the different states of vibration of a particle at two different instants. It is represented as:

ΔΦ = Φ2 – Φ1

The phase difference is defined as the time gap between two or more waves that can be either fall behind or leads in correspondence to one another. Phase difference is a characteristic of a single wave and it is the relative characteristic of two or more waves. It is also identified as either offset or angle. This is generally symbolized by the letter Ф. The entire phase of the wave is shown as 2π.

Path Difference (Δx) or (x)

Path difference means the distance between two points along the direction of propagation of the wave through the medium.

It is referred as the difference in distance between the source and the observer. To determine both the constructive and destructive wave interference, path difference is generally used.

Relationship Between Path Difference and Phase Difference

Phase difference and path difference are directly proportional to each other. Let us suppose there are two waves having the same frequency, then phase difference and path difference is related as –

Δx = Δϕλ/2π

Where,

Δx = path difference

Δϕ = phase difference

Different Between Path Difference and Phase Difference

The difference between Path difference and Phase difference is described below:

Path Difference vs Phase Difference
Properties	Phase difference	Path difference
Definition	Phase difference means the difference in the phase angle of two waves.	Path difference means the difference in the path travelled by two waves.
Symbol	Δϕ	Δx
Unit	Radian or Degree	Metre
Formula	Δϕ = 2πΔx/λ	Δx = Δϕλ/2π

Read More,

• Wave Properties
• Wave Optics
• Ray Optics

Wave Motion: Frequently Asked Questions

What is Wave Motion in Sound?

Wave motion in sound refers to the propagation of sound waves through a medium, such as air, water, or solids. Sound waves are longitudinal mechanical waves, which means that the particles of the medium vibrate back and forth in the direction parallel to the direction of wave propagation.

What is Difference Between Particle and Wave Motion?

Particle motion refers to the movement of individual particles, such as atoms, molecules, or objects, through space whereas Wave motion involves the propagation of energy through a medium or space without the transfer of matter.

What are Three main Type of Wave Motion?

The three main type of wave motion are:

• Mechanical Waves
• Electromagnetic Waves
• Matter Waves

What is Wave Motion?

Wave motion refers to the energy and momentum traveled from one point to another point in vacuum or medium ( solid,liquid or gas) without changing the matter’s property by motion.

What are Main Characteristics of Wave Motion?

The main characteristics of the wave motion are as follows:

• In a medium, the particles vibrate about their mean positions.
• The speed of a wave motion depends upon the nature of the medium through which it moves.
• Energy, pressure and momentum etc are transferred from one point of the medium to another point. During this transfer, there is no movement of the matter.

What is Relationship Between Speed, frequency and Wavelength of Wave Motion?

The relationship between the speed, frequency and wavelength of a wave is,

Speed (Velocity ) = Frequency × Wavelength

What is Amplitude of Wave Motion?

Amplitude of a wave is the maximum displacement of any particle of the medium from its original or mean position. For describing the size of wave, amplitude is used.