Which statement correctly distinguishes sound power from sound intensity?

• A. Sound power is per unit area; sound intensity is the total power of the source
• B. Sound power is the total amount of sound produced by a source (in Watts); sound intensity is power per unit area (Watts per square meter)
• C. They are the same quantity
• D. Sound intensity is measured in decibels

Answer: (B)

Sound power is the total acoustic energy a source emits per unit time, an intrinsic property of the source with units of watts. Sound intensity is the power crossing a unit area, so it depends on how the sound spreads and how far you are from the source, with units of watts per square meter. For a point source radiating equally in all directions, intensity drops with distance as I = P / (4πr^2), even though the total power P from the source stays the same. This is why the correct statement says sound power is the source’s total power (in watts) and sound intensity is power per unit area (in watts per square meter). The other options aren’t correct because they either swap the definitions, claim they’re the same quantity, or mislabel the unit (decibels measure level, not the basic unit of intensity).