Which expression correctly defines the wavelength λ given the speed of sound c and frequency f?

• A. λ = f / c
• B. λ = c × f
• C. λ = c − f
• D. λ = c / f

Answer: (D)

Wavelength comes from how fast the wave travels and how often its cycles occur. The basic relation v = f λ links speed v to frequency f and wavelength λ, so rearranging gives λ = v / f. For sound, v is c, so λ = c / f. This makes sense because at a fixed speed, increasing frequency produces a shorter wavelength.

The other forms aren’t valid because they mix units or signs: f / c would have wrong units for a length, c × f combines speed with frequency to give a dimensional result that isn’t a length, and c − f combines incompatible units. Only c / f yields a length consistent with wavelength.