Longitudinal Waves - Examples, Diagram, FAQs

In this article, we define longitudinal wave, longitudinal wave direction, longitudinal movement, and longitudinal vibration. It includes examples of longitudinal waves, with illustrations.
Note: Longitudinal meaning in Hindi is अनुदैर्ध्य

What is a longitudinal wave?

Waves can be classified into two types based on the direction of particles relative to the direction of the wave travel. They are longitudinal waves and transverse waves.

The wave illustration of the two types of waves can be observed in the figure below.

Figure 1 Wave illustration of longitudinal and transverse waves

A wave consisting of a periodic vibration traveling in the same direction as the direction that the wave travels is called a longitudinal wave. From the above figure, the longitudinal wave is a wave in which particle displacement is parallel to the direction of wave propagation.

A wave in which the particle displacement is perpendicular to the direction of wave propagation is called a transverse wave.
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What is longitudinal vibration?

If the direction of the particles present in the shaft moves parallel to the axis of the shaft then it is called longitudinal vibration.

Explain longitudinal waves with diagrams.

In figure 2, a longitudinal wave in the air is represented graphically. The longitudinal wave image below is a graph of distance from source versus density of air. Particles are denser at a particular region on the curve. It is called the compression region and it is present on the top of the curve. The region where particles are less crowded is called rarefaction. It is present at the bottom of the curve. In the compression region, particles are close to each other while they part away in rarefaction. Peaks represent maximum compression and rarefaction.

Figure 2 A longitudinal wave in the air

Define longitudinal direction.

The direction that is parallel to the direction of the long axis of a body is called longitudinal direction.

The velocity of longitudinal wave:

Longitudinal waves transmit through media with some velocities. The velocity of the wave depends on the elasticity and density of the substance.

In solids, the velocity of a longitudinal wave is given by,

Here, E is Young’s modulus and ρ is the density of the substance.

In liquids, the velocity of a longitudinal wave is given by,

Here, B is the bulk modulus and ρ is the density of the fluid.

Examples for longitudinal wave:

The longitudinal wave includes examples such as sound waves, seismic P-waves, ultrasound waves, etc.

The wavelength of longitudinal wave:

The distance between two successive compressions or between two successive rarefactions is called the wavelength of a longitudinal wave. It estimates the size of waves.

Figure 3 Sound wave

The above figure represents a sound wave which is also a longitudinal wave. The wavelength, amplitude, and velocity of the longitudinal wave are shown in the diagram.

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Amplitude: When the wave compresses particles in the medium, the distance between those particles is called the amplitude of the wave. It can also be stated as the distance between the equilibrium position of the medium and the compression or rarefaction. Waves produced by greater energy of disturbance produce greater amplitude.

Frequency: Frequency is the number of wavelengths per second. Frequency remains constant regardless of the change in speed.

Sound wave:

If the particles are denser at a particular region in the sound wave, then it is compression in the sound wave. If those particles are separated then it is called rarefaction in the sound wave.

The motion of a sound component is measured from its equilibrium position as it produces sound waves. The distance measured is called displacement in a sound wave. The displacement and pressure in a sound wave are interrelated. Pressure in a sound wave is either maximum or minimum when its displacement is zero. If the neighbouring particles are nearer to the point then maximum pressure is observed. So, minimum pressure is observed when neighboring particles are away from the point.

Wave energy transfer diagram:

The vibration of particles is the reason for energy transfer in waves. It can be seen in different forms of the wave. In sound waves, the periodic vibration of air particles is responsible for energy transfer. The vibrations of electric and magnetic fields cause energy transfer in electromagnetic waves. Energy transfer is done by the vibration of water particles in water waves.

The motion of particles is perpendicular to the horizontal movement of the wave. The energy transfer is done in between the kinetic and potential energy of the wave.

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Difference between longitudinal wave and transverse wave:

Longitudinal and transverse waves are differed by following:

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