# Frequency of sound problem

1. Mar 28, 2012

### 40856

What frequency of sound traveling in air at 11 oC has a wavelength of 4 m?

From what I can come up with... the frequency of sound at 20C is 344 m/s and at -20C is 320 m/s. From this I interpolated and got at 10C it is 332 m/s and then kinda guessing at 11C it is 333.2 m/s.

333.2 / 4 m = 83.3 hz

...thoughts? My main question revolves around my interpolation of the speed of sound in air at 11C

2. Mar 28, 2012

### nasu

You can use one of the formulas for the speed of sound in air as a function of temperature, to check your interpolation.
For example, see formulas here
http://en.wikipedia.org/wiki/Speed_of_sound

The first approximation is of course a linear increase so your value should be close, if done correctly. I don't understand why would you interpolate at 10 degrees first, if you need it at 11.
From your data, there is change of 24m/s for a temperature change of 40 degrees. This means 0.6m/s/degree. So it will be (320+0.6*31)m/s at 11 degrees (31 degrees above -20).

3. Mar 28, 2012

### 40856

Ok I see your point. Doing it that way, I come up with speed of sound at 11C = 338.6.

338.6/4m = 84.65