Which of the following is an example of a longitudinal wave?

• A. Light waves propagating through a vacuum
• B. A wave on the surface of water
• C. Waves on a stretched string
• D. Sound waves traveling through air

Answer: (D)

Verified step by step guidance

1. Understand the difference between longitudinal and transverse waves: In longitudinal waves, the particle displacement is parallel to the direction of wave propagation, while in transverse waves, the displacement is perpendicular to the direction of propagation.
2. Analyze each option by considering the direction of particle motion relative to wave propagation: For light waves propagating through a vacuum, the oscillations are electromagnetic and transverse in nature.
3. For a wave on the surface of water, the particles move in circular or elliptical paths, which is characteristic of surface waves, not purely longitudinal.
4. For waves on a stretched string, the displacement of the string is perpendicular to the direction the wave travels, making them transverse waves.
5. For sound waves traveling through air, the air particles oscillate back and forth in the same direction as the wave travels, which is the defining feature of longitudinal waves.