A rarefaction is the region in a longitudinal wave where particles are spread apart. Particles in a rarefaction are further from each other than in their undisturbed positions.
Rarefactions alternate with compressions. Together, one compression and one rarefaction make up one complete wavelength.
In a sound wave travelling through air, rarefactions correspond to regions of lower air pressure. The ear’s eardrum moves outward during a rarefaction and inward during a compression.
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