As a general observation about media, sound propagates faster in materials with greater:

As a general observation about media, sound propagates faster in materials with greater:

• A. Compressibility
• B. Acoustic impedance
• C. Stiffness
• D. Refractive index

Answer: (C)

Sound speed in a medium depends on how stiff the material is and how dense it is. When a material is stiffer, the restoring forces acting on the particles after they’re displaced are stronger, so the disturbance passes from one particle to the next more quickly. In solids this relation is often summarized by v ≈ sqrt(E/ρ), where E is a measure of stiffness and ρ is density. Since compressibility is the inverse of stiffness, more compressible materials allow slower wave propagation. Acoustic impedance depends on both speed and density and doesn’t set the speed by itself, and refractive index relates to light, not sound. So greater stiffness yields faster sound propagation.

Sound speed in a medium depends on how stiff the material is and how dense it is. When a material is stiffer, the restoring forces acting on the particles after they’re displaced are stronger, so the disturbance passes from one particle to the next more quickly. In solids this relation is often summarized by v ≈ sqrt(E/ρ), where E is a measure of stiffness and ρ is density. Since compressibility is the inverse of stiffness, more compressible materials allow slower wave propagation. Acoustic impedance depends on both speed and density and doesn’t set the speed by itself, and refractive index relates to light, not sound. So greater stiffness yields faster sound propagation.