# A Pipe filled with Helium

1. Nov 9, 2008

### kristibella

1. The problem statement, all variables and given/known data
A certain organ pipe, open at both ends, produces a fundamental frequency of 291 Hz in air.

If the pipe is filled with helium at the same temperature, what fundamental frequency fHe will it produce? Take the molar mass of air to be 28.8 g/mol and the molar mass of helium to be 4.00 g/mol.

2. Relevant equations
fHe = v/$$\gamma$$

$$\gamma$$ = 2 L

3. The attempt at a solution
Honestly, I have no idea what to do with this problem so I have no attempt. I was completely thrown off my the molar masses because I haven't seen a problem like this before. I'm not even sure if these are the right formulas for this problem.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 9, 2008

### LowlyPion

The speed of sound will be different in helium from that of air.

For ideal gasses:
http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/souspe3.html

For helium:
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html#c5

3. Nov 10, 2008

### kristibella

Thank you so much! I wasn't sure if the speed of sound had anything to with this. Those websites were extremely helpful and I quickly got to the correct answer of 854.5 Hz.