Identifying compression in longitudinal waves

Steps:

• Recall that in a longitudinal wave, compressions occur where particles are displaced towards each other, increasing density.
• Examine the graph: it plots particle displacement from equilibrium versus distance from the source at a fixed instant.
• Identify regions of maximum density: these are where adjacent particles have displacements that bring them closer together.
• Locate the center: it's the point of zero displacement midway between particles moving inward, indicating peak compression.

Why B is correct:

• Point B shows zero displacement at the midpoint of a region where particles on either side are displaced towards it, matching the definition of maximum density in a compression.

Why the others are wrong:

• A: Represents a rarefaction center, with particles displaced away, decreasing density.
• C: Lies on a positive displacement slope, indicating ongoing particle motion, not peak compression.
• D: Shows negative displacement, part of a rarefaction or antinode, not compression.

Final answer: B