The total power of ultrasound is measured in which unit?

The total power of ultrasound is measured in which unit?

• A. Watts
• B. Joules
• C. Newtons
• D. Pascals

Answer: (A)

Power is the rate at which energy is delivered per unit time. In ultrasound therapy, the transducer sends energy into the tissue, and the total acoustic power represents how much energy is delivered each second. That makes the appropriate unit watts (W), since 1 watt equals 1 joule per second. Joules measure total energy (not the rate), Newtons are a unit of force, and pascals measure pressure. So they don’t quantify how quickly energy is being delivered. If you later talked about energy delivered over a period, you’d use joules; if you discussed energy per area, you’d use intensity (W/cm²).

Power is the rate at which energy is delivered per unit time. In ultrasound therapy, the transducer sends energy into the tissue, and the total acoustic power represents how much energy is delivered each second. That makes the appropriate unit watts (W), since 1 watt equals 1 joule per second.

Joules measure total energy (not the rate), Newtons are a unit of force, and pascals measure pressure. So they don’t quantify how quickly energy is being delivered. If you later talked about energy delivered over a period, you’d use joules; if you discussed energy per area, you’d use intensity (W/cm²).