For a traveling ultrasonic wave, wavelength equals velocity divided by frequency. Which expresses this relationship correctly?

• A. Wavelength = Velocity ÷ Frequency
• B. Wavelength = Velocity × Frequency
• C. Wavelength = Frequency ÷ Velocity
• D. Wavelength = 1 ÷ (Velocity ÷ Frequency)

Answer: (A)

Wavelength is the distance the wave travels during one cycle. The speed v is how fast the wavefront moves, and the frequency f is how many cycles occur each second. In one second, the wave covers v meters, and there are f cycles, so one cycle spans v/f meters. This makes wavelength equal to velocity divided by frequency. Checking units reinforces this: meters = (meters per second) ÷ (per second) = meters. The other expressions don’t give a length in meters (they mix units or take reciprocals), so they don’t represent wavelength.