Which term describes the dependence of velocity on frequency?

Which term describes the dependence of velocity on frequency?

• A. Dispersion
• B. Amplitude
• C. Energy
• D. Density

Answer: (A)

Dispersion describes the dependence of velocity on frequency. In a dispersive medium, different frequency components travel at different speeds, so a pulse changes shape as it propagates (pulse broadening). This can involve phase velocity varying with frequency, and often group velocity as well. In ultrasound practice, tissues are treated as largely nondispersive at diagnostic frequencies, so velocity is assumed constant with frequency; dispersion becomes important in media with frequency-dependent relaxation or other complex properties. The other terms—amplitude, energy, and density—relate to how strong a wave is, how much energy it carries, and how much mass per volume the medium has, but they do not describe how velocity changes with frequency.

Dispersion describes the dependence of velocity on frequency. In a dispersive medium, different frequency components travel at different speeds, so a pulse changes shape as it propagates (pulse broadening). This can involve phase velocity varying with frequency, and often group velocity as well. In ultrasound practice, tissues are treated as largely nondispersive at diagnostic frequencies, so velocity is assumed constant with frequency; dispersion becomes important in media with frequency-dependent relaxation or other complex properties. The other terms—amplitude, energy, and density—relate to how strong a wave is, how much energy it carries, and how much mass per volume the medium has, but they do not describe how velocity changes with frequency.