In which type of wave do particles move perpendicular to the direction of propagation?

• A. Longitudinal
• B. Transverse
• C. Surface
• D. Circular

Answer: (B)

In a transverse wave, the particles of the medium oscillate perpendicular to the direction the wave is moving. This means as the wave travels forward, the medium’s displacement is up and down (or side to side), not along the travel direction. A rope waved up and down is a classic example: the wave propagates along the rope, while the individual segments move perpendicular to that direction. The same perpendicular relationship appears in electromagnetic waves, where electric and magnetic fields oscillate at right angles to the direction of propagation.

Longitudinal waves have particle motion parallel to the wave’s travel, seen as compressions and rarefactions along the direction of travel, so they don’t fit the perpendicular criterion. Surface waves involve motion that can be circular or elliptical near the surface, not a strict perpendicular displacement, and circular waves describe a more complex motion than a simple perpendicular relationship.