In a longitudinal wave, energy is transferred in a direction that is $—$ to the direction of the wave's movement.

• A. $\mathrm{opposite}$
• B. $\mathrm{perpendicular}$
• C. $\mathrm{at} a 45° \mathrm{angle}$
• D. $\mathrm{parallel}$

Answer: (D)

Verified step by step guidance

1. Understand the nature of a longitudinal wave: in such waves, the particles of the medium oscillate back and forth in the same direction as the wave travels.
2. Recall that energy transfer in a wave occurs through the motion of particles in the medium, so the direction of energy transfer aligns with the particle oscillation direction.
3. Since in a longitudinal wave the particle oscillations are along the direction of wave propagation, the energy transfer must also be in the same direction.
4. Contrast this with transverse waves, where particle motion is perpendicular to wave propagation, and energy transfer is also perpendicular.
5. Therefore, conclude that in a longitudinal wave, energy is transferred parallel to the direction of the wave's movement.