At an interface between two different materials, an impedance difference results in:

• A. Reflection of the entire incident energy at the interface
• B. Absorption of sound
• C. Division of sound energy into transmitted and reflected modes
• D. None of the above

Answer: (C)

When an acoustic wave meets an interface between two materials with different impedances, the boundary conditions require part of the energy to be reflected back into the first material and part to be transmitted into the second material. This division of energy into reflected and transmitted waves is the fundamental outcome of impedance difference. The exact amounts depend on how different the impedances are, but the key point is that energy is split rather than all being reflected or all being transmitted. Absorption can occur as the wave travels through a material, but the primary effect at the interface itself is the creation of both a reflected and a transmitted wave. Therefore, the energy is divided into transmitted and reflected modes.