Sharing thoughtful approaches to teaching physics with the wider world.
IOPSpark Sound resources
11 June 2019 at 13:54 #59672
I am delivering my “Tones Tines and Tings” talk at the IOP South West Physics CPD Day
So I am exploring the new https://spark.iop.org
Beats feature in my talks. The talk this time will have a new audience participation time, with whistling lollipops given to each member of the audience. We will try and make a beat frequency together.
The first thing I found on IOPSpark was a SPT classroom activity using audacity. There is a nice way to use audacity with a police whistle to explore ghost frequencies.
Here are some of the ways I demonstrate beats
You can use two signal generators
It is probably unlikely to have two signal generators so you can do a similar thing with mobile phones.
The first way I ever made beats was with two tuning forks.
13 June 2019 at 10:53 #59685
What never ceases to amaze me about physics is when you look at a concept you will always find an application for it somewhere!
To test for poisonous gases in mines they used to have organ pipe with surface air in it and another with air pumped up from the mine. These pipes of same length were played together. If one pipes frequency was changed due to the gas from the mine being of a different density then a beat was heard.
We used to use beats to tune our cornets in Frodsham Silver Band.
14 June 2019 at 12:25 #59720
My son made me this Audacity tutorial to make beats.
Audacity is a free, open source, cross-platform audio software
The link below is to the PowerPoint
Another resource on the IOP Spark website is Practical Activity 14 – 16 Nuffield Practicals.
Here beats are in the Introducing Waves page
14 June 2019 at 12:50 #59723
Some times the path difference questions are based on waves other than EM waves.
This question is how I became aware of Quincke’s tube. The instructions to make it are here
25 June 2019 at 13:28 #59806
I found this clip of one in action
This tube is sometimes called a Herschel-Quincke tube (HQ tube). Usually it is the second name in the double named phenomenon that is lost over time, like Lorentz-Fitgerald contraction. Like I said above with the application of beats in finding poisonous gases in mines. Every time you look in to an effect or phenomenon in physics you find someone has made use of it. I discovered that the HQ tube is used in jet engines to try and remove certain frequencies that are much loader spikes than the general engine rumble.
This images came from this document
HQ tube interference 2
I also found a NASA manual for the Honeywell TFE 731-60 jet engine.
This was an interesting document. The last page has the security classification of the document.
Still amazes me that such a simple concept as path difference being used to cancel out the sound with destructive interference.
25 June 2019 at 13:54 #59807
Another way I have seen sound of a particular frequency being reduced is using a Helmholtz resonator.
25 June 2019 at 14:52 #59810
I have a collection of Helmholtz resonators
My favourite use of my vodka bottles came from a Marvin and Milo card.
You can find Marvin and Milo on the new IOPSpark website
You can hear with the same amount of water in each bottle the same tone. I am using an effervescent powder.
At 0.40 seconds in the video I blow across the top of the fizzing bottle and you can it does not really resonate as the bottom surface is no longer reflecting the sound from a smooth plane surface. It is important to let the water settle down. Now you have one bottle filled with carbon dioxide and one with air. The more dense carbon dioxide gives a noticeably lower tone.
26 June 2019 at 20:04 #59815
Thanks for all these great ideas- I built the Quincke’s tube today to use with my Y12s!
I have a question- why does the pitch drop for the CO2 bottle? (struggling to think of an explanation!)
27 February 2020 at 21:39 #62118
When you blow across the top of the bottle you compress the gas and the gas springs back like a mass spring system. The denser gas moves backwards and forwards slower. The equation for the speed of sound (compression rarefaction) in an ideal gas is
The bigger the mass the slower the speed.
You must be logged in to reply to this topic.