Standing waves on strings

First harmonic frequency (f) = 1/2L(T/m) Second harmonic frequency (f) = 1/L(T/m) Fourth harmonic frequency (f) = 4/2L(T/m)

A string can be made to vibrate in a selected harmonic by plucking it at one point (the antinode) to give a large initial amplitude and touching it at another (the node) to prevent vibration at that point.