Which statement is true regarding transducer diameter and divergence?

• A. Larger diameter yields less divergence
• B. Larger diameter yields more divergence
• C. Diameter does not affect divergence
• D. Only frequency affects divergence

Answer: (A)

Beam divergence comes from diffraction at the emitting aperture. A transducer acts as a circular aperture, so the main beam width is roughly proportional to lambda divided by the aperture diameter (lambda/D). Increasing the diameter while keeping the wavelength the same makes the beam spread less, producing a narrower, less divergent beam. That’s why a larger transducer diameter yields less divergence.

Note that frequency also affects divergence because it changes the wavelength (lambda = c/f). Higher frequency (shorter wavelength) reduces divergence for a given diameter, but the statement in question specifically links diameter to divergence, and increasing diameter indeed reduces divergence. The other options are not correct: a larger diameter does not increase divergence, and divergence is not controlled by frequency alone.