Use the formula: ( f = dfrac{v}{lambda} )
( f ) = frequency
( v ) = wave speed
( lambda ) = wavelength
For light in vacuum: ( f = dfrac{c}{lambda} )
( c = 3.0 times 10^8 , text{m/s} )
Make sure wavelength is in meters
Make sure wave speed is in meters per second
Divide wave speed by wavelength to get frequency in hertz
Example: ( lambda = 2 , text{m} ), ( v = 10 , text{m/s} ), ( f = 5 , text{Hz} )