Longitudinal and Transverse Waves

What is a Wave?

A disturbance that causes a transfer of energy from one point to another through a medium is a wave. This energy is the motion of particles and this motion is passed on to the neighboring particles by vibrations. This does not imply that the particles of the medium move from one place to another, instead vibrate at their positions. A wave has many properties like frequency, amplitude, and wavelength. Transverse waves and Longitudinal waves are two waves that are classified based on vibrations of particles of the medium. Let us discuss Transverse and Longitudinal waves in detail in this article. 

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Transverse Waves

When the particles vibrate perpendicular to the direction of propagation of a wave, it is known as the transverse wave. These waves possess the property of perpendicular motion. Particles transport energy by moving at right angles with the direction of the wave. The neighboring particles move in opposite directions. These waves can be experienced in real life when a wood log creates ripples on the surface of a water body.

Transverse Waves constitute moving crests ( or peak), and troughs. A crest is the highest point whereas a trough is the lowest point. In crest, a particle displaces upward from its original position and thus shown by the top point(peak) in the above figure whereas in the trough, a particle displaced downward from its original position and shown by the bottom point(valley) in the above figure. These propagate only through solids.


Longitudinal Waves

When the particles vibrate along the direction of propagation of a wave, it is known as the longitudinal wave. These waves possess the property of parallel motion. Particles transport energy by moving along the direction of the wave. These waves can be experienced in real life when a spring is compressed or stretched along its length.

Due to the motion of particles, a pressure variation is caused in the medium which leads to compressions (high-pressure areas) and rarefactions (low-pressure areas).

Compression occurs when particles of the medium come close to each other, and thus vibrate and create high-pressure regions and rarefaction occurs when the particles vibrate away from each other creating low-pressure regions.


Sound Waves

Sound waves are longitudinal in nature. This is because when it travels in air, the particles move back and forth, and the pressure of the air changes, hence giving birth to a longitudinal wave.

One important thing about sound waves is that it can only travel through a medium. There is an easy experiment to prove this: An electrical bell is fitted in a jar with a vacuum. When the bell rings, the person standing outside cannot hear it as sound has no medium to travel.

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The speed of sound waves depends on the medium. As the particles of the medium are closer in a denser medium, the vibrations travel fast. This is the reason why sound travels about faster in water than air. Properties of sound waves decide the nature of the sound-

  • High-frequency sounds are shrill and low-frequency sounds are flat.

  • High amplitude sounds are loud and low amplitude sounds are soft.

  • The quality of a sound separates sounds from different instruments that have the same frequency and amplitude.


Difference Between Transverse and Longitudinal Waves

Transverse Waves

Longitudinal Waves

Particles vibrate at right angles to the direction of propagation of the wave.

Particles vibrate back and forth along the direction of propagation of the wave.

Can be propagated through solids only

Can be propagated through all states of matter

Generally slower in nature

Generally faster than the transverse waves

Contains crests and troughs

Contains compressions and rarefactions

Position of particles is measured through time.

Pressure variation is measured through time.

Light waves are transverse 

Sound waves are longitudinal


Did You Know?

  • Electromagnetic waves do not require a medium to travel and that is how we receive light from the sun.

  • The human ear is sensitive to only pressure variations and thus sound waves are longitudinal in nature.

  • Dogs can hear higher frequency sounds and therefore can hear noises we humans cannot hear.

  • Light travels with a speed of 3,00,000 km/sec through the air.

  • The velocity of light is the fastest and no particle could travel faster than it.

  • The speed of sound in water is about 4 times the speed of sound in air.

  • Light behaves both as a wave and as a particle from time to time.

  • Supersonic planes are aircraft that travel faster than the speed of sound and cause shock waves.

  • Opera singers sing in very high-frequency waves and hence can shatter a glass.

  • Waves traveling in the same medium superimpose and the net displacement of the particle is the sum of individual displacements of the waves.

FAQs (Frequently Asked Questions)

1. Is Light transverse or longitudinal and how?

Ans. Light has both the parts of energy i.e. electric and magnetic and hence is called an electromagnetic wave. All electromagnetic waves are transverse. Light waves do not require a medium to travel and transfers both electrical and magnetic energy. Light has different wavelengths and thus shows different colors for specific ranges of wavelengths. Wavelength is the distance between two consecutive crests or troughs. Light waves travel in a straight direction which is called linear propagation of light.

2. How are Waves formed in a string?

Ans. Particles of a string are confined and move perpendicular to the wave direction and hence these are transverse waves. These vibrations have peaks and troughs. Multiple waves are produced in a string that forms standing waves. A standing wave is a combination of 2 waves in opposite directions. Their energies either cancel out or add together.