Which equation relates speed, frequency, and wavelength?

• A. Speed = Frequency x Wavelength
• B. Speed = Wavelength / Frequency
• C. Speed = Frequency / Wavelength
• D. Speed = 1/(Frequency x Wavelength)

Answer: (A)

Think about how far the wave travels each second. Frequency is how many cycles occur per second, and wavelength is the distance covered in one cycle. If there are f cycles every second and each cycle spans λ meters, then the distance traveled in one second is f × λ, which is the speed. That’s why the equation is v = fλ. The units also line up: hertz (s⁻¹) times meters gives meters per second, the standard unit of speed. For a quick check, a sound wave at 440 Hz with a wavelength of about 0.78 m would have a speed of 440 × 0.78 ≈ 343 m/s, matching the typical speed of sound in air.