How Does Helium Affect the Fundamental Frequency of an Organ Pipe?

[kristibella]

Homework Statement

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 f_He 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.

Homework Equations

f_He = v/$$\gamma$$

$$\gamma$$ = 2 L

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.

 

[LowlyPion]

Homework Statement

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 f_He 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.

Homework Equations

f_He = v/$$\gamma$$

$$\gamma$$ = 2 L

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.

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

 

[kristibella]

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

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.