# Beat frequency in organ pipe

#### dimpledur

1. The problem statement, all variables and given/known data

Chapter 12, problem 34. An auditorium has organ pipes at the front and at the rear of the
hall. Two identical pipes, one at the front and one at the back, have fundamental frequencies
of 264.00 Hz at 20.0°C. During a performance, the organ pipes at the back of the hall are at
25.0°C, while those at the front are still at 20.0°C. What is the beat frequency when the two
pipes sound simultaneously? Use 3 significant figures.

3. The attempt at a solution

Basically, I am not sure whether to assume the organ pipes are closed at one end, and open at the other, or open at both ends. My textbook says it can be both...

Anyways, what I was going to do was just take a ratio of the frequencies.

f1 / f2 = (n1*v1/4L) / (n2*v2/4L)

The only problem here is I have 2 unknowns. I don't know n2 or f2..

#### Delphi51

Homework Helper
I think you would use n1 = n2 = 1 since it mentions fundamental frequency.
Do you understand why the pipe at the back would have a different frequency due to the higher temperature there?

The temperature affects the speed of sound in the air inside the pipe, so v2 will be different from v1. You will need a formula that tells how the speed of sound varies with temperature.

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