Which equation correctly expresses wavelength as propagation speed divided by frequency?

• A. Wavelength = Propagation speed × Frequency
• B. Wavelength = Propagation speed / Frequency
• C. Wavelength = Frequency / Propagation speed
• D. Wavelength = 1 / Frequency

Answer: (B)

The key idea is how wavelength relates to propagation speed and frequency. A wave travels a distance equal to its speed each second, and it has f cycles every second. If each cycle spans a distance λ, then in one second the wave covers f × λ meters. That distance per second is the propagation speed v, so v = f λ. Rearranging gives λ = v / f. This shows why dividing the speed by the frequency yields wavelength: doubling the speed while keeping frequency the same doubles the wavelength, and doubling the frequency with the speed fixed halves the wavelength. The other forms would not match the actual relationship and would mix up the units or physical meaning (for example, 1/f is the period, not the wavelength).