← all cardsTopic 11 · Wave Motion · Definitions
Compression & rarefaction
● VERBATIM — examined word-for-wordCompression: region of a longitudinal wave where particles are closest together — pressure above normal. Rarefaction: furthest apart — pressure below normal. (Not "refraction".)
What this actually means
Compression: neighbours have converged, so density and pressure sit above normal. Rarefaction: neighbours have spread out, pressure below normal.
Watch the spelling: rarefaction, not 'refraction'. Different word, different chapter, real marks lost.
C and R are regions of the medium, not peaks of the displacement graph. They sit at zero displacement, which the longitudinal section makes precise.
Prove it — watch it be true
- Watch a compression halo: particles bunched, Δp positive
- Watch a rarefaction halo: particles spread, Δp negative
- Check the Δp–x graph: peaks at C, troughs at R