Sound, light, and radio-frequency (RF) electromagnetic waves differ in their propagation characteristics. Here are some key distinctions:
Nature: Sound waves are mechanical waves that require a medium (such as air, water, or solids) for propagation. They result from the compression and rarefaction of molecules within the medium. Light and RF waves, on the other hand, are electromagnetic waves that can propagate through vacuum as well as through various media. They consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.
Speed: Sound waves propagate relatively slowly compared to light and RF waves. The speed of sound depends on the properties of the medium through which it travels, such as its density and elasticity. In air at room temperature, sound travels at approximately 343 meters per second (about 767 miles per hour). Light waves travel much faster, with a constant speed of approximately 299,792,458 meters per second (about 671 million miles per hour) in a vacuum. RF waves, being a form of electromagnetic radiation, also travel at the speed of light.
Wavelength and Frequency: Sound waves have longer wavelengths, ranging from centimeters to meters, which correspond to their low frequencies in the audible range. Light waves have much shorter wavelengths, ranging from hundreds of nanometers (visible light) to picometers (X-rays and gamma rays). RF waves have even longer wavelengths, ranging from millimeters to kilometers, depending on their frequency bands.
Interaction with Matter: Sound waves interact strongly with matter and can be reflected, refracted, absorbed, or diffracted by various objects and media. Light waves and RF waves also interact with matter but exhibit different behaviors. Light waves can be reflected, refracted, absorbed, or transmitted by different substances, and their interaction can lead to phenomena like scattering and polarization. RF waves can penetrate certain materials, depending on their frequency, and can be reflected, refracted, or absorbed by objects and structures.
As for why sound is not considered a true wave phenomenon, it is because sound waves require a medium for propagation. They rely on the mechanical vibrations and oscillations of particles within the medium to transmit energy. In contrast, electromagnetic waves, such as light and RF waves, are self-propagating and can travel through a vacuum without the need for a medium. They are governed by Maxwell's equations and exhibit wave-like behavior, including interference, diffraction, and polarization.