Difference Between Sound Waves and Electromagnetic Waves

In modern day world, there are many scientific and technological applications of different kinds of waves. Most of such applications use sound waves or electromagnetic waves. Sound waves are mechanical waves whereas electromagnetic waves are not mechanical waves. Therefore, sound waves require a medium for their propagation whereas electromagnetic waves do not require a medium. This is the main difference between sound waves and electromagnetic waves. There are many other differences between these two. This article tries to explicate them in detail.

What is a Sound Wave

Sound waves are mechanical waves produced by mechanical vibrations. For an example, when your phone rings, it vibrates its surrounding, generating compression and rarefaction in the air. These compression and rarefaction propagate through air. When they reach our eardrum, they cause the eardrum to vibrate; this is what we perceive as a sound. They require a material medium for the propagation as they are mechanical waves. Therefore, sound waves cannot travel through a vacuum.

Sound waves propagate through air, liquids, and plasma as longitudinal waves. In solids, on the other hand, sound waves can propagate as both longitudinal waves and transverse waves. Anyhow the speed of sound depends on the material properties. In the air, the speed of light increases with the temperature.

For our convenience, sound waves are classified into three bands as below.

Infrasound – Frequencies below 20Hz

Audible sound – Frequencies between 20Hz and 20000Hz

Ultrasound – Frequencies above 20000Hz

Longitudinal sound waves cannot be polarized as only transverse waves can be polarized.

Further, sound waves mainly characterized by their pitch, loudness, and quality.

What is an Electromagnetic Wave

Electromagnetic waves are produced by accelerating or decelerating charged particles. They are transverse waves. As a result, electromagnetic waves are polarizable. Electromagnetic waves unlike any other types of waves contain a magnetic field and also, an electric field oscillating perpendicular to each other and perpendicular to the direction of propagation of the wave. These waves carry energy in the direction of propagation of the wave. They can propagate through a vacuum as they are not mechanical waves. They can propagate through air, liquids, or solids. Anyhow, electromagnetic waves attenuate while they are traveling through a material medium. The degree of attenuation depends on the material properties of the medium through which the electromagnetic waves propagate. In a vacuum, electromagnetic waves travel with 3×10⁸ms^-1. In any material medium, the speed of the waves and their wavelengths decreases.

The frequencies of electromagnetic waves have an extremely broad range. The properties of waves depend on the frequency, amplitude, etc. Therefore, for our convenience, electromagnetic waves are grouped into several bands namely radio waves, microwaves, infrared, light, UV, X-rays and γ rays. Altogether, the entire range is called the electromagnetic spectrum.

Difference Between Sound Waves and Electromagnetic Waves

Formation

Sound waves: Sound waves are produced by mechanical vibrations.

EM waves: EM waves are produced by accelerating (or decelerating) charged particles.

Sources

Sound waves: Sound waves are created by musical instruments, speakers, tuning forks, etc.

EM waves: EM waves are created in Current carrying wires, blackbody radiation.

Speed in vacuum

Sound waves: Sound cannot propagate through a vacuum.

EM waves: EM waves travels with the speed of ms^{-1 .}

Speed in air

Sound waves: Speed of sound in air increases with the temperature.

EM waves: Speed of EM waves in air is slightly slower than that of in a vacuum.

Polarization

Sound waves: Longitudinal sound waves aren’t polarizable.

EM waves: EM waves are Polarizable.

Atomic Excitation

Sound waves: Sound waves cannot excite atoms.

EM waves: EM waves can excite atoms.

Sensation produced

Sound waves: Sound waves produce hearing.

EM waves: EM waves produces seeing.

Applications

Sound waves: There are many applications including musical instruments, ultrasound scanning, ultrasound cleaning, sonar devices, in mineral explorations, in petroleum explorations, in consumer electronics and for hearing.

EM waves: There are hundreds of applications. In general, those applications are listed under the relevant bands of the electromagnetic spectrum because most of the applications depend on the frequency of the EM waves.

Radio waves-Radio broadcasting etc.

Microwaves- microwave oven, TV, mobile phones, etc.

Infrared remote controls.

Visible light- vision, photosynthesis,

Ultra violet-UV- visible spectroscopy

X- Rays- diagnostic X-ray imaging in medicine, X-Ray crystallography.

γ- Rays-radiotherapy, to sterilize medical equipment.

Image Courtesy:

“Electromagnetic waves” by P.wormer – Own work, (CC BY-SA 3.0) via Wikimedia Commons

“Sound waves” by Luis Lima89989 – Own work (CC BY-SA 3.0) via Wikimedia Commons