# Homework Help: Harmonics frequency problem

1. Aug 18, 2009

### dance_sg

1. The problem statement, all variables and given/known data
A small town’s noon hour whistle is an air column 0.750 m long and closed at one end. Find the fundamental frequency and the next harmonic produced by this whistle when the speed of sound in air is 342 m/s.

2. Relevant equations
f= v/λ,

3. The attempt at a solution
would i first find the frequency, then divide that by 3 to get the 3rd harmonic? then take the same number i divided by 3, but divde it by two to find the second harmonic?

2. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

In the closed pipe, length of the pipe for the fundamental frequency is equal to λ/4.
The next harmonics is three times the fundamental frequency.

3. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

so divide 0.750m by 4 to find the fundamental frequency? then how would i find the necxt harmoinic?

4. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

No.
λ = 4* length of the tube.

5. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

so im multiplying the wavelength by 4...

6. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

No. In the problem the length of the tube is given, not the wavelength.
If you see the stranding wave in the tube closed at one end, you can see that length of then tube is equal to λ/4.

7. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

so how do i solve for the wavelength then?

8. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

Wavelength = 4*length of the tube.

9. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

0.750 x 4 then..

10. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

Use the relevant formula which you have mentioned, and find the frequency.

11. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

ok. so that would be the frequency. in the question tho it says find the next harmonic. how do i do that?

12. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

Next frequency is equal to three times the fundamental frequency.

13. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

ok. so multiply what i got for the frequency by 3.

14. Aug 18, 2009

### rl.bhat

Re: harmonics&frequency

Yes.

15. Aug 18, 2009

### dance_sg

Re: harmonics&frequency

thank you so much