Rubens tube physics project

[KEØM]

For a Physics project my group and I are trying to build a Rubens tube. It is a device that shows the standing waves inside a closed-closed tube using fire. We are putting a small speaker inside a pvc pipe that is perforated on the top with holes. We will then fill the tube with propane and then light each hole so that you can see a flame. We then will turn on the speaker and if the standing wave formula is satisfied the flame heights will change and the flames form an image of the standing waves. My question is for the standing wave equation

f = mv/2L

can we assume that the speed of sound is 343 m/s or because of the higher temperature inside the tube and because of a different gas (propane) will we need to calculate the speed of sound ourselves?

Any help will be greatly appreciated.

Thanks,
KE0M

 

[jbsteele]

LEIn this case, it would be best to calculate the speed of sound yourself. The speed of sound is affected by temperature and pressure, so the speed of sound in your Rubens tube will likely be different than the speed of sound in air at sea level (343 m/s). You can use the speed of sound equation to calculate the speed of sound in your tube: v=sqrt((γ*R*T)/M) where γ is the adiabatic index, R is the universal gas constant, T is the absolute temperature, and M is the molecular weight of your gas (in this case, propane).

 

[nlightner]

That sounds like a really interesting project! The Rubens tube is a great way to visualize standing waves and their frequencies. To answer your question about the speed of sound, it is true that the speed of sound can vary depending on the temperature and type of gas. In this case, the temperature inside the tube may be slightly higher than the surrounding air, but the difference should be minimal. As for the gas, propane has a slightly higher speed of sound compared to air, but again, the difference should not be significant.

In general, the speed of sound in a gas can be calculated using the formula:

v = √(γRT/M)

Where:
- v is the speed of sound
- γ is the adiabatic index of the gas (1.4 for air, 1.1 for propane)
- R is the gas constant (8.314 J/mol·K)
- T is the temperature in Kelvin
- M is the molar mass of the gas (28.97 g/mol for air, 44.1 g/mol for propane)

So, if you want to be very precise, you could calculate the speed of sound using this formula. However, for your project, using the approximate speed of sound in air (343 m/s) should be sufficient. Keep in mind that the main purpose of this project is to demonstrate the concept of standing waves and the relationship between frequency, wavelength, and tube length. The slight variation in speed of sound should not significantly affect your results.

I hope this helps and good luck with your project!