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

• A. Water wave on the surface of a pond
• B. Light wave in vacuum
• C. Radio wave
• D. Sound wave in 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: Water waves on the surface of a pond involve particles moving in circular or elliptical paths, which is characteristic of surface waves (a combination of longitudinal and transverse components), but primarily transverse on the surface.
3. Light waves in vacuum and radio waves are electromagnetic waves, which are transverse waves because their electric and magnetic fields oscillate perpendicular to the direction of propagation.
4. Sound waves in air are pressure waves where air particles oscillate back and forth along the direction the wave travels, making them longitudinal waves.
5. Therefore, identify the sound wave in air as the example of a longitudinal wave because the particle motion is parallel to the wave direction.