Which expression correctly represents the wavelength of soft-tissue sound given frequency in MHz?

Which expression correctly represents the wavelength of soft-tissue sound given frequency in MHz?

• A. Wavelength (mm) = 1.54 mm / Frequency (MHz)
• B. Wavelength (mm) = Frequency (MHz) / 1.54 mm
• C. Wavelength (mm) = 1.54 mm * Frequency (MHz)
• D. Wavelength (mm) = 1.00 mm / Frequency (MHz)

Answer: (A)

The main idea is that wavelength is found from dividing the speed of sound by frequency, and in soft tissue the speed is about 1540 m/s. When frequency is given in megahertz, convert units so the result is in millimeters: λ = c/f becomes λ(mm) = (1540 m/s) / (f(MHz) × 10^6 s⁻¹), then convert meters to millimeters by multiplying by 1000, giving λ(mm) = 1.54 / f(MHz). So the expression that matches this is wavelength in millimeters equal to 1.54 mm divided by the frequency in megahertz. Using any form that multiplies by frequency or uses a 1.00 mm constant would not align with the inverse relationship or the standard soft-tissue speed, so those would produce incorrect results.

The main idea is that wavelength is found from dividing the speed of sound by frequency, and in soft tissue the speed is about 1540 m/s. When frequency is given in megahertz, convert units so the result is in millimeters: λ = c/f becomes λ(mm) = (1540 m/s) / (f(MHz) × 10^6 s⁻¹), then convert meters to millimeters by multiplying by 1000, giving λ(mm) = 1.54 / f(MHz). So the expression that matches this is wavelength in millimeters equal to 1.54 mm divided by the frequency in megahertz.

Using any form that multiplies by frequency or uses a 1.00 mm constant would not align with the inverse relationship or the standard soft-tissue speed, so those would produce incorrect results.