Sound waves and Temperatures

[Vybe]

Currently going through some concepts in TBR Physics.

There was an example about a sound wave going through 2 Pipes, Pipe A and Pipe B. In trials, it showed that Pipe A had larger frequencies in subsequent harmonics (1,2,3). The answer said it was because of the increasing temperature in Pipe A as opposed to Pipe B. Increased temperature causes gases to move faster, thus, moving the sound wave through Pipe A quicker; which amounts to why there is higher frequency readings.

My question is, doesn't increase in temperature cause gases to have higher viscosity? Higher viscosity amounting to slower movement of waves such as sound waves?

Not sure If I am incorrectly integrating those two concepts together. Would like some feedback. Thanks

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[gettheleadout]

I no longer have my TBR books but if I correctly recall the question and what you mean by "larger frequencies," (meaning greater magnitude in Hz) then I think this was one where TBR messed up. The temperature of the air in the pipes would affect the speed of the sound waves but not their frequency.

 

[Vybe]

So their wavelengths would increase?

This wasn't a particular problem it was an example problem in the book.

And I understand its logical to think that increased temperature would increase speed of sound waves. But what is the exact science behind it? Thanks

 

[DrknoSDN]

Temperature is a measure of average kinetic energy of molecules in a gas. If you increase the temperature you increase the random molecular velocities. If the molecules are all moving faster, when a sound wave causes them to propagate out, it will take less time for them to strike the next molecule (faster wave propagation).

 

[gettheleadout]

So their wavelengths would increase?

Yes, they would, since at a constant frequency the wave speed and wavelength are directly proportional.

 

[Vybe]

Yes, they would, since at a constant frequency the wave speed and wavelength are directly proportional.

So, when sound waves go from a medium such as air to a medium such as water, all that increases drastically is wavelength? To increase speed from 340 m/s to 1500 m/s? Just making sure.

Also...

How would this relate to electromagnetic waves or light waves going from 1 medium to another.. how do those change? Only wavelength as well?

Best,

 

[NextStepTutor_1]

Yes, when moving from one medium to another, the (sometimes large) difference in speed is caused by an increase in wavelength. For electromagnetic waves, remember that when EM waves move from a medium to another, more denser medium, the speed decreases, and the wavelength also decreases as well. The frequency is constant for both cases.