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

[GreenMind]

Homework Statement

A certain organ pipe, open at both ends, produces a fundamental frequency of 275 Hz in air.

If the pipe is filled with helium at the same temperature, what fundamental frequency f 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

below

The Attempt at a Solution

v(he)=999 m/s
v(O)=344 m/s
I solved with $$fn = n v / 2 L$$ but I am not getting as accurately of an answer as id like. How can I incorporate the molar mass into these equations?

 

[Dick]

You'll need to find the relationship between the speed of sound in an ideal gas to the density of the gas. The density is proportional to the molar mass.

 

[denverdoc]

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