In which type of wave does the medium travel parallel to the direction of wave propagation?

• A. Longitudinal Wave
• B. Transverse Wave
• C. Surface Wave
• D. Standing Wave

Answer: (A)

The key idea is how the medium moves as the wave passes. In this type, the particles of the medium oscillate back and forth along the same line that the wave is traveling. That back-and-forth motion creates regions where the medium is compressed and then stretched as the wave moves forward. Sound waves traveling through air are the classic example of this behavior.

In contrast, for a transverse wave the particles move perpendicular to the direction the wave travels, like a rope moving up and down while a wave moves horizontally. Surface waves involve motion that isn’t simply along the travel direction; near the surface the particles can move in circular or elliptical paths. Standing waves are patterns formed by the interference of waves, producing stationary nodes and antinodes rather than a description of particle motion along the propagation direction.