Answer: Compression.
- A Crest
- B Trough
- C Rarefaction
- D Compression
Correct answer: D. Compression
Explanation: In longitudinal waves, compression is a region where particles are closer together (higher pressure); rarefaction is lower pressure.
A standing wave forms from two identical waves travelling in opposite directions and interfering; nodes (always zero displacement) and antinodes (maximum displacement) stay fixed in place, unlike a travelling wave where the whole pattern moves.
Concept context
Wave types, superposition, standing waves, Doppler effect, and sound intensity.