Further elaboration: I’m wondering if sound waves have sizes in the same way that the electromagnetic spectrum does. Like how visible light can’t reflect off viruses because they are too small. Is it like that with sound?
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Yes, all waves (including sound waves) have “sizes”, but “sizes” needs some unpacking here.
A wave is a periodic disturbance in… *something*. The wave’s “amplitude” is the magnitude of the maximum disturbance from the *something’s* mean value. The wave’s “wavelength” is the distance between the peaks of the disturbance in the *something*. Both of these could be called measures of the wave’s “size”. (The other defining characteristics of a wave are its frequency and its speed, but these can’t really be described as the “size” of the wave, so I’ll ignore these.)
I’ll take three cases, getting less intuitive as we go.
In **water waves**, the disturbance (in… water) is at right-angles to the wave’s direction of travel. The amplitude is the maximum distance (in metres) between the peak height of the water and the water’s mean height. The wavelength is the distance (in metres) between peaks.
In **sound waves**, the disturbance is a pressure wave – periodic compression in the packing of the constituent particles of some medium (air, water, solids) where the disturbance is in the same direction as the wave’s direction of travel. (The usual analogy is to a Slinky being pushed to get a compression in the coils travelling along the toy’s length.) The simplest and most direct measure of amplitude for sound waves is the difference in pressure of the air (or other medium) between its maximum and mean levels as the pulse of pressure passes. (For the Slinky, it would be the increased packing density of the coils.) With sound, we normally express amplitude indirectly – as a measure of loudness (in decibels). The wavelength is the distance (in metres) between points of maximum compression in the medium.
In **electromagnetic waves (e.g. light)**, things get trickier, because we’re no longer talking about a disturbance in a physical medium; we’re now talking about a disturbance in an electric field. (There’s also a paired magnetic field, but we can stick to the electric field for this example.) As with water waves, the disturbance is at right-angles to the wave’s direction of travel and the wavelength is the distance (in metres) between peaks in the disturbance. The amplitude of the wave is the maximum disturbance in the electric field. This is most directly measured in newtons per coulomb, or in volts per metre. For light, an increase in amplitude results in a higher intensity (brightness) of the light (measured in candelas).
(Edit to clarify section on amplitude of sound waves.)
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