Which factor does NOT affect impedance?

Which factor does NOT affect impedance?

• A. Stiffness
• B. Density
• C. Propagation speed
• D. Frequency

Answer: (D)

Impedance in a homogeneous medium for mechanical waves depends on how easily the medium resists motion as the wave travels. In the simple, ideal case, impedance is Z = ρ c, where ρ is density and c is the wave speed. The wave speed itself is determined by stiffness (and density), for example c increases with greater stiffness. So both density and stiffness influence impedance, via their effect on c. Frequency does not appear in the basic relation, so changing frequency doesn’t alter impedance in this ideal model. (Note: real materials with damping can show some frequency dependence, but the fundamental concept uses impedance as independent of frequency.)

Impedance in a homogeneous medium for mechanical waves depends on how easily the medium resists motion as the wave travels. In the simple, ideal case, impedance is Z = ρ c, where ρ is density and c is the wave speed. The wave speed itself is determined by stiffness (and density), for example c increases with greater stiffness. So both density and stiffness influence impedance, via their effect on c. Frequency does not appear in the basic relation, so changing frequency doesn’t alter impedance in this ideal model. (Note: real materials with damping can show some frequency dependence, but the fundamental concept uses impedance as independent of frequency.)