Which property would increase propagation speed of sound through a medium?

• A. Increased stiffness
• B. Increased density
• C. Increased frequency
• D. Increased distance

Answer: (A)

Sound speed in a medium is determined by how easily the material can transmit a disturbance from one part to the next. A stiffer medium resists deformation more strongly, so when one region is displaced, it pushes the neighboring region more forcefully and quickly, speeding up the wave’s travel. In many cases, the speed of a longitudinal wave scales with the square root of stiffness (elastic modulus) divided by density, so increasing stiffness raises speed, while increasing density adds inertia and slows it down. Frequency doesn’t set the propagation speed in a uniform medium, it mainly affects wavelength; distance only changes how far the wave must travel, not how fast it goes. Therefore, increasing stiffness is the factor that increases propagation speed.