Energy transmission depends on density changes during which wave phases?

• A. Compression only
• B. Rarefaction only
• C. Both compression and rarefaction
• D. Neither compression nor rarefaction

Answer: (C)

Energy transmission in a wave comes from the way the medium’s density and pressure oscillate as the wave passes. In a sound wave, parcels of the medium move back and forth along the direction of travel, creating regions where the medium is compressed (higher density) and regions where it is rarified (lower density). The energy carried by the wave is tied to these density and pressure fluctuations—the pattern of high-density and low-density regions moves through the medium, transmitting energy as it goes. Since energy transfer relies on changes in density, and both compressed and rarefied regions involve density changes, energy is carried by both phases. If only one phase mattered, the wave could not propagate continuously; the alternating compressions and rarefactions work together to sustain energy transport.