Rayleigh waves are best described as waves that:

• A. Travel along the surface with combined longitudinal and transverse motion
• B. Propagate through the bulk with purely longitudinal motion
• C. Always travel faster than longitudinal waves
• D. Cannot exist in coarse-grained metals

Answer: (A)

Rayleigh waves are surface waves that travel along the free surface of an elastic solid. Near the surface, particle motion consists of a mix of longitudinal and shear displacements, producing elliptical motion that decays with depth into the material. Because the energy is concentrated in the near-surface region, Rayleigh waves travel more slowly than bulk longitudinal or shear waves, which is why they are especially useful for inspecting surface and near-surface features.

This description fits best because it captures the surface-bound nature and the combined motion of Rayleigh waves. The other statements describe bulk P-waves (purely longitudinal motion), claim a speed relationship that isn’t true (Rayleigh waves are not faster than bulk waves), or assert nonexistence in metals that isn’t correct.