Which two characteristics affect the speed of sound in a medium?

Which two characteristics affect the speed of sound in a medium?

• A. Frequency and Wavelength
• B. Temperature
• C. Density and Stiffness
• D. Impedance

Answer: (C)

Sound speed in a medium depends on how stiff the material is and how much mass there is per unit volume. A stiffer medium resists compression more strongly, so the restoring forces act quickly and the wave travels faster. A denser medium has more inertia, which slows the motion of the particles and reduces the speed. In fluids, speed is roughly the square root of stiffness (bulk modulus) divided by density; in solids, it's related to elastic modulus over density. That’s why sound moves slowest in air, faster in water, and can be very fast in stiff solids like steel. Frequency and wavelength don’t set the speed directly; they are linked by v = fλ, while impedance involves density and speed but doesn’t determine the speed itself.