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Standing waves in open organ pipes

General formula for wavelength,
31165.png [where n = 1, 2, 3, …]
Fig. 10
  • First normal mode of vibration: n1 = 31052.png
    This is called fundamental frequency and the note so produced is called fundamental note or first harmonic.
    Fig. 11
  • Second normal mode of vibration:
    This is called second harmonic or first overtone.
    Fig. 12
  • Third normal mode of vibration: 30676.png, n3 = 3n1
    This is called third harmonic or second overtone.
Some Important Points
In an open organ pipe all harmonics are present whereas in a closed organ pipe, only alternate harmonics of frequenciesn1, 3n1, 5n1, …, etc., are present. The harmonics of frequencies 2n1, 4n1, 6n1, …, are missing. Hence, musical sound produced by an open organ pipe is sweeter than that produced by a closed organ pipe.
Fig. 13
  • Harmonics are the notes/sounds of frequency equal to or an integral multiple of fundamental frequency (n). Thus, the first, second, third, harmonics have frequencies n1, 2n1, 3n1, … .
  • Overtones are the notes/sounds of frequency twice/thrice/ four times the fundamental frequency (n), e.g., 2n, 3n, 4n, …, and so on.
  • In organ pipe, an antinode is not formed exactly at the open end rather it is formed a little distance away from the open end outside it. The distance of antinode from the open end of the pipe is known as end correction.

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