Frequency and wavelenght
Wave length: In the longitudinal waves, The distance between two consecutive compression or rare fractions of a sound wave is called wave length (). Same as the transverse wave, it is defined as the distance between two consecutive crests or troughs of a transverse wave.
Frequency: It is the number of vibrations or cycles produced by source of wave per second, called frequency. If seven crest of a wave is produced in one second, then it is said that the frequency of the wave is 7 cycles or vibrations per second. It’s SI unit is Hertz (Hz). SO frequency of waves is 7 Hz.