# Homework Help: Sound wave.

1. Feb 16, 2008

### azatkgz

1. The problem statement, all variables and given/known data
When you sing, the vocal folds in your throat act as a resonating cavity (one open end, one closed end) which allows only certain frequencies. Suppose you try to sing a pure tone which is detected by a microphone and measured to have a frequency 500.0 Hz. This is the resonance frequency of the vocal folds in your throat, which only depends on the tension and mass of the flesh in your vocal folds. If you now replace the air of density 1.000 kg/m3 with helium of density 0.1640 kg/m3, what frequency will the microphone measure? Provide a graphical representation of the standing waves in your throat. You may assume that the bulk modulus remains constant in the two cases, and that only the density changes.

3. The attempt at a solution
I think if we change the medium to helium,it will change only wavelenth.

So Frequancy remains constant.

2. Feb 16, 2008

### ||spoon||

If the speed remains constant then the frequency will change...

V=fw

V-velocity
f-frquency
w-wavelength

I dont know if the speed changes or not though, my intuition says that the frequency will increase because when you inhale helium your pitch of your voice increases

3. Feb 16, 2008

### CaptainQuasar

That's not all that will change, it will sound hilarious now. :tongue2:

But seriously, as ||spoon|| notes, if wavelength changes without velocity changing at the same time, frequency has to change.

4. Feb 16, 2008

### azatkgz

Then if we change the medium velocity will change,right?
Velocity of sound wave in the should be faster.
From V=fw
If velocity increases then wavelength also.Frequancy remains constant.
Is it Right?