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Physics LibreTexts

2.2: Activities

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  • Things You Will Need

    All you will need for this lab is this PhET simulator. Go ahead and run this simulator now in another window for use in the activities below.

    Creating Harmonics

    In the previous lab, you may have calculated the traveling wave velocities for the three tension settings in this simulator. There is no need to do these again, or to go back and look them up – here they are for you to use:

    Low tension setting:        \(v_{wave} = 1.25 \frac{cm}{s}\)

    Medium tension setting: \(v_{wave} = 3.75 \frac{cm}{s}\)

    High tension setting:      \(v_{wave} = 6.25 \frac{cm}{s}\)

    1. The Background Material shows a step-by step method for creating a standing wave with three antinodes between two fixed ends. Your first task is to repeat this process to create a standing wave with the same number of antinodes for each of the other two tensions. For each of these two tensions, do the following:
      1. Provide a screen capture (or a photo, if you are unable to do this) of the standing wave in the simulator. Be sure to include the control panel at the bottom of the screen that shows the frequency you used for the standing wave, and the tension setting.
      2. In your lab report, show the calculations you performed to determine how to create the standing wave.
    2. Select the "Rulers" box in the lower-right corner, and use the vertical ruler to measure the amplitude of one of the standing waves you created (you don't need to do both of them). It will of course help to freeze the simulator, and step it until the maximum displacement of the antinode is achieved (recall you can also move the ruler where you like). Record the measurement (no screen capture necessary), and explain how this value is the correct one according to the standing wave mathematics we have seen.
    3. Create a standing wave with any tension that keeps all of the green beads stationary. As before:
      1. Provide a screen capture of the standing wave in the simulator.
      2. In your lab report, show the calculations you performed to determine how to create the standing wave.

    One End Free

    In principle we can also create standing waves with the string having a free end. Select the "Loose End" radio button in the top-right corner.

    1. It turns out that we can only approximate such a standing wave with this simulator, because the frequency setting only goes to two decimal places. Explain why at least 3 decimal places are required to get a precise standing wave on this simulator.
    2. Try approximating a standing wave with a loose end with a rounded-off frequency that should get you close. Submit a screen capture of your attempt.

    Lab Report

    Download, print, and complete this document, then upload your lab report to Canvas. [If you don't have a printer, then two other options are to edit the pdf directly on a computer, or create a facsimile of the lab report format by hand.]