A hydrophone is used to measure which property?

• A. Velocity
• B. Frequency
• C. Intensity
• D. Phase

Answer: (B)

A hydrophone acts like a tiny underwater microphone that senses acoustic pressure fluctuations in the medium. It directly converts those pressure changes into an electrical signal. Because you capture how pressure varies over time, you can analyze the waveform to see how rapidly the pressure oscillates, which is the frequency of the ultrasonic wave. Other properties like velocity (particle motion), intensity (which depends on both pressure and impedance), or phase (which requires a reference) aren’t the direct measurements provided by a basic hydrophone. So the most straightforward and primary thing you obtain with a hydrophone is the frequency of the sound.