<Dd> ψ (r, t = 0) = A e i k ⋅ r, (\ displaystyle \ psi (\ mathbf (r), \ t = 0) = A \ e ^ (i \ mathbf (k \ cdot r)) \,) </Dd> <P> where the wavelength is determined by the wave vector k as: </P> <Dl> <Dd> λ = 2 π k, (\ displaystyle \ lambda = (\ frac (2 \ pi) (k)) \,) </Dd> </Dl> <Dd> λ = 2 π k, (\ displaystyle \ lambda = (\ frac (2 \ pi) (k)) \,) </Dd>

A sound wave is often called a pressure wave