What is the wavelength equation in ultrasound physics?

• A. wavelength = frequency / velocity
• B. wavelength = velocity × frequency
• C. wavelength = velocity / frequency
• D. wavelength = 1 / velocity

Answer: (C)

Wavelength is determined by how fast the sound travels in the medium and how often it repeats per second. The correct relationship is that wavelength equals the speed of sound divided by the frequency. In soft tissue, the speed is about 1540 m/s, so with a 5 MHz transducer the wavelength is roughly 0.31 mm. This means higher frequency gives shorter wavelengths (better axial resolution) but less penetration due to greater attenuation. Other forms don’t yield a length: for example, multiplying speed by frequency mixes units to something not a distance, and dividing or taking reciprocals would produce non-length units.