Period is determined by the ______.

• A. Medium properties
• B. Transducer design
• C. Operator
• D. Sound source only

Answer: (D)

Period is the time for one complete cycle, so it’s set by how fast the source is vibrating. That frequency from the sound source fixes T = 1/f. The medium can change how fast the wave travels and thus its wavelength, but it doesn’t change the time between successive cycles produced by the source. The transducer and how the signal is delivered affect coupling and efficiency, not the rate at which cycles are emitted. So the period is determined by the sound source alone. For example, driving at 2 MHz yields a period of 0.5 microseconds, regardless of whether the wave travels through air or tissue; the speed changes with the medium, but the cycle interval stays the same.