If we increase the frequency, the near zone length is:

If we increase the frequency, the near zone length is:

• A. increased
• B. decreased
• C. unchanged
• D. depends on transducer

Answer: (A)

Increasing frequency lengthens the near field. The near zone length for a transducer with a given aperture depends on wavelength roughly as Z ∝ D^2/λ. Since wavelength λ equals the speed of sound c divided by frequency f, increasing frequency shortens λ and → Z grows. In practice, using a higher frequency pushes the point where the beam becomes more planar further away from the transducer, so the near field extends farther. The other options don’t fit because they would require the wavelength to increase (decreasing frequency) or suggest no change, whereas changing frequency directly alters the near-field extent. Saying it depends on the transducer ignores the explicit frequency effect on wavelength that governs the near zone.

Increasing frequency lengthens the near field. The near zone length for a transducer with a given aperture depends on wavelength roughly as Z ∝ D^2/λ. Since wavelength λ equals the speed of sound c divided by frequency f, increasing frequency shortens λ and → Z grows. In practice, using a higher frequency pushes the point where the beam becomes more planar further away from the transducer, so the near field extends farther.

The other options don’t fit because they would require the wavelength to increase (decreasing frequency) or suggest no change, whereas changing frequency directly alters the near-field extent. Saying it depends on the transducer ignores the explicit frequency effect on wavelength that governs the near zone.