The direction relation of particle motion to wave propagation for shear waves produced by immersion angulation is:

• A. Parallel to wave propagation
• B. Perpendicular to wave propagation
• C. Normal to surface
• D. Tangential to surface

Answer: (B)

Shear waves are transverse, so the particles move in a direction perpendicular to how the wave travels. When you generate a shear wave in immersion testing by angling the probe, the wave still propagates in one direction while the particle displacement is perpendicular to that direction. So the correct description is that particle motion is perpendicular to the wave propagation. Statements about motion being parallel to travel describe longitudinal waves, and phrasing like normal or tangential to a surface relates to orientation to the surface rather than the fundamental relationship to propagation.