Which mechanism causes energy to be redirected back toward the source when encountering a boundary?

• A. Absorption
• B. Scattering
• C. Refraction
• D. Reflection

Answer: (D)

When a wave meets a boundary, one key outcome is that energy can bounce back toward where it came from—that's reflection. In reflection, the wavefront bounces off the boundary and travels back, with the angle of incidence equal to the angle of reflection relative to the boundary’s normal. This bouncing behavior is why mirrors and calm water surfaces send energy back toward you. Absorption would convert energy to heat with little forward or backward flow, scattering spreads energy in many directions, and refraction bends the path as the wave enters a new medium—none of these specifically send energy back toward the source.