Organ pipes are the musical instrument which are used for producing musical sound by blowing air into the pipe. Longitudinal stationary waves are formed on account of superimposition of incident and reflected longitudinal waves.

Equation of standing wave y = 2a cos

(1) First normal mode of vibration :

This is called fundamental frequency. The note so produced is called fundamental note or first harmonic.

(2) Second normal mode of vibration :

This is called third harmonic or first overtone.

(3) Third normal mode of vibration : 

This is called fifth harmonic or second overtone.

Position of nodes : x = 0,