Which factor does not affect impedance?

Which factor does not affect impedance?

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

Answer: (B)

In wave propagation through a uniform, lossless medium, impedance is the opposition the medium offers to the passage of a wave, and it’s defined as the ratio of pressure (or stress) to particle velocity. For a plane wave, impedance is Z = ρc, where ρ is density and c is the wave speed. The speed c depends on the material’s stiffness and density (for example, c ≈ sqrt(E/ρ) in a solid or sqrt(K/ρ) in a fluid), so impedance is intrinsically tied to density and stiffness (through c) and thus to the propagation speed itself. Frequency, by contrast, does not alter Z in this ideal model; the relationship p = Zu holds with Z constant for all frequencies. Only in real, damped or dispersive materials would impedance vary with frequency. So, frequency is the factor that does not affect impedance.

In wave propagation through a uniform, lossless medium, impedance is the opposition the medium offers to the passage of a wave, and it’s defined as the ratio of pressure (or stress) to particle velocity. For a plane wave, impedance is Z = ρc, where ρ is density and c is the wave speed. The speed c depends on the material’s stiffness and density (for example, c ≈ sqrt(E/ρ) in a solid or sqrt(K/ρ) in a fluid), so impedance is intrinsically tied to density and stiffness (through c) and thus to the propagation speed itself. Frequency, by contrast, does not alter Z in this ideal model; the relationship p = Zu holds with Z constant for all frequencies. Only in real, damped or dispersive materials would impedance vary with frequency. So, frequency is the factor that does not affect impedance.