What is the fundamental relationship between speed, frequency, and wavelength in ultrasound?

• A. Speed = Wavelength / Frequency
• B. Speed = Frequency - Wavelength
• C. Speed = Frequency x Wavelength
• D. Speed = Frequency + Wavelength

Answer: (C)

In ultrasound, how fast the wave moves is the product of how often cycles occur and how far the wave travels in one cycle. A single cycle spans one wavelength, and the wave repeats f cycles each second, so the distance covered per second (speed) is v = f × λ. This relation also means that for a given medium, speed is constant, so increasing the frequency shortens the wavelength (λ = v/f). That’s why higher-frequency ultrasound gives better axial resolution but less depth penetration due to attenuation. The other forms aren’t correct because they mix quantities with different units or don’t yield a speed when you multiply frequency (1/s) by wavelength (m).