Standing waves

Content, content, content, when will we fit in the assessed practicals, content, content, how close are the exams? content, is how most of my classes are going at the moment.

I’ve been teaching year 12 about standing waves. We’ve looked at some good demos.

Melde’s experiment gave them a great visualisation of standing waves. Some had been struggling to imagine what the stationary wave attend looked like and this waves on a stretched string experiment provided a ‘got it!’ moment for some students.

After this we tried to measure the speed of light using a microwave and some processed cheese slices.

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I love this experiment for its grand aim, using  basic equipment. It uses the fact that a standing wave pattern is set up in the microwave. You can use the points that melt first on the cheese to measure the distance between anti-nodes, and so calculate the wavelength of the microwaves.

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Combine this with the frequency of the microwaves (find it on the back of the microwave) and you can calculate the speed of the waves. Love it!

We didn’t get a great value this time. The biggest problem being the plate we used. It wasn’t flat and I think this complicated it.

We have also looked at standing waves in pipes. Disappointed that our Rijke tube couldn’t be located *sniff*.

The whole waves unit is now finished. I have a pile of end of unit tests to mark. Hope to see some good results!

 

 

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3 Responses to Standing waves

  1. Matt says:

    This is one of my favourite topics to teach! I hadn’t see the Rijke tube before. Great talking points.

    Resonance tubes are a lovely way of teaching standing waves and easy to make. You can quite easily graph it to get the speed of sound out too, and because you have to process in order to get a straight line graph it helps generate an understanding of the equation for a tube open at one end, as well as preparation for the assessed pracs.

    The method’s here:
    http://hyperphysics.phy-astr.gsu.edu/hbase/class/phscilab/restube2.html

    Then, of course, there’s the Ruben’s tube. We’re lucky in that a geeky student was determined to make one, and spent half of last year building it after school. Again, lots of talking points and a visual representation of the pressure differences.

    Oh, and have you ever plucked a guitar under the strobe? Hypnotising!

    Like

  2. audsley says:

    Thanks for you comment. I always show a Ruben’s tube video, but I’m sure it’s not the same as having the real thing! Very jealous! 🙂

    Like

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