Impedance is a characteristic of ______.

• A. The boundary
• B. The source
• C. The medium only
• D. Both media

Answer: (C)

Impedance describes how a wave meets resistance as it travels, and it is determined by the medium through which the wave propagates. In acoustics, the impedance is the ratio of pressure to particle velocity, Z = p/u, and for simple plane waves it simplifies to Z = ρc, where ρ is density and c is the speed of sound. This shows that impedance is set by the medium’s properties, not by the boundary or the source alone. The boundary affects what part of the wave is reflected or transmitted via impedance mismatch, but the impedance itself is a property of the medium. The source can have its own impedance, influencing how the wave is launched, but it does not define the medium’s impedance. Saying it belongs to both media isn’t accurate because each medium has its own characteristic impedance, and the concept here refers to the medium’s property.