Question

To determine a waves' frequency, you must know the

Answer 1

velocity of wave and wavelength
velocity=wavelength*frequency
i.e V=L*f
f=V/L

Answer 2

its time period

Answer 3

For reference:\[\large f = freq, v = velocity, \lambda = wavelength, p = period, T = time\]
The wave equation is defined as:\[\large v=\frac{\lambda}{p}\]Knowing that period is defined as:\[\large p=\frac{1}{f}\]You can rewrite the wave equation as as:\[\large v=\lambda f\]Rearrange that to see that:\[\large f=\frac{v}{\lambda}\]So you need to know the wavelength and the velocity to determine a wave's frequency.