What does determine the harmonic number in standing waves?

[brainyman89]

what does determine the harmonic number in standing waves?

 

[maverick_starstrider]

Think of the biggest (largest wavelength) standing wave you can fit in your boundary conditions (open at both ends, open at one end, closed at both ends), this is harmonic number 1 (the fundamental frequency). For one end open it's 1/4 a wavelength, for both open or both closed it's 1/2 a wavelength. Then draw the second biggest you can, that's the second harmonic (3/4 a wavelength for one end open, 1 wavelength for both closed/open). Then the third biggest (third harmonic), etc. This is the harmonic number

 

[brainyman89]

i know what is harmonic number, i was asking about what determines it, for example in a pipe, whether it is of one or two openings, who decide what the harmonic number is i.e can we control it?? why does the first harmonic occur and not the second or vice versa?

thanks for answering

 

[maverick_starstrider]

it's the first, second, third, etc. largest wave that fits the boundaries. That IS what determines it.

 

[AlephZero]

The standing wave needs a force applied at the correct frequency, to replace the energy lost by damping etc.

In a lab experiment you usually apply a force at one frequency only, so you can only get a standing wave at the that frequency.

In real-world situations there is no reason why you can't have several standing waves simultaneously, and in fact that is usually what happens.