Sound waves are which of the following?

• A. Electric
• B. Mechanical, Transverse
• C. Spectral
• D. Longitudinal, Mechanical

Answer: (D)

Sound waves are mechanical disturbances that require a medium to carry energy. In medical ultrasound, the wave travels as a longitudinal wave, meaning the particle motion is in the same direction as the wave’s travel, creating alternating areas of compression and rarefaction. This distinguishes them from electric (electromagnetic) waves, which don’t need a medium, and from purely spectral descriptions that talk about frequency content rather than how the wave moves through matter. While some mechanical waves in solids can be transverse, ultrasound through tissue is described most accurately as longitudinal and mechanical, which is why this option is the best fit.