The places where particles of the medium spread farther apart are called rarefactions.

Quick Scoop: What That Means

In a longitudinal wave (like a sound wave in air), the particles of the medium move back and forth in the same direction the wave travels. As they do this, two key regions form:

  • Compressions – particles are packed close together, pressure and density are higher.
  • Rarefactions – particles are spread farther apart , pressure and density are lower.

So, when your question says “places where particles of the medium spread farther apart” , that is exactly the definition of rarefactions in a longitudinal wave.

In many middle-school and high-school wave diagrams, compressions are drawn as close-together lines, and rarefactions as widely spaced lines, showing where the medium is least crowded.

Answer to use in class or homework:
Places where particles of the medium spread farther apart are called rarefactions.

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