In a longitudinal wave, which region describes particles that are spread apart?

In a longitudinal wave, which region describes particles that are spread apart?

• A. The compression
• B. Rarefaction
• C. The crest
• D. The wavelength

Answer: (B)

In a longitudinal wave, particles move back and forth in the same direction as the wave travels, creating alternating regions of higher and lower particle density. The region where particles are pressed together is a compression, while the region where they are spread apart is a rarefaction. Rarefaction describes the parts of the wave where particles are more sparse, which is why it is the term for the region described as spread apart. A crest belongs to transverse waves, which have vertical displacements, not the back-and-forth motion of longitudinal waves. Wavelength is a distance measure—how far the pattern repeats—not a region itself. Rarefaction.

In a longitudinal wave, particles move back and forth in the same direction as the wave travels, creating alternating regions of higher and lower particle density. The region where particles are pressed together is a compression, while the region where they are spread apart is a rarefaction. Rarefaction describes the parts of the wave where particles are more sparse, which is why it is the term for the region described as spread apart. A crest belongs to transverse waves, which have vertical displacements, not the back-and-forth motion of longitudinal waves. Wavelength is a distance measure—how far the pattern repeats—not a region itself. Rarefaction.