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Physics LibreTexts

7.2: Activities

  • Page ID
    23051
  • Things You Will Need

    Nothing! All the data has been meticulously collected for you.

    Salvaging Your Data

    The purpose of this lab is to confirm Faraday's law, and your lab assistant collected data for you, using the apparatus described in the Background Material. He performed four separate runs at four different values for the oscillation current frequency \(f\) through the field coil, and four different current amplitudes \(I_o\). The current as a function of time in each case had the form:

    \[I\left(t\right) = I_o\cos\left(2\pi ft\right) \]

    For each run, your lab assistant took a photograph of the computer's graph of current vs. time, and a photograph of the oscilloscope's output. Unfortunately your lab assistant had a few... um... issues.

    • He wasn't careful in his use of the oscilloscope. In particular, he didn't use the vertical or horizontal adjustment to the axes, which makes reading values a bit difficult, and he did not use consistent knob settings. So you have to be careful about extracting numbers from what is shown in the o-scope output.
    • He paired-off the pictures for each run, but didn't label them or staple the pairs together. And – you guessed it – he dropped the pile of papers before giving them to you, and now all the pictures are scrambled, which means you now need to reconstruct the data before testing Faraday's law with it.

    The Data

    Before we get to the pictures, we'll list all of the constant values that come from the apparatus, and are therefore the same for every run.

    • field coil
      • radius \(= R = 0.157m\)
      • number of turns in coil \(= N = 100\) 
    • detector coil
      • radius \(= r = 0.013m\)
      • number of turns in coil \(= n = 1000\)

    Now for the pictures. First the graphs from the computer, labeled A, B, C, D for future reference:

     computer_graphs.png

    And now the oscilloscope outputs, labeled 1, 2, 3, 4 for future reference:

    o_scopes_1_2.png

    o_scopes_3_4.png

    Data Analysis

    1. Salvage the error by your lab assistant by matching the A – D pictures to the corresponding 1 – 4 pictures. [Hint: How do the functional forms of \(I\left(t\right)\) and \(\mathcal E\left(t\right)\) compare with each other?]
    2. For all four runs, use the readout from the oscilloscope picture (and of course the specifications of the field and detector coils given above) to compute the maximum current in the field coil, then confirm that this number lands close to the value in the corresponding computer picture.
    3. Estimate the percent uncertainty of the oscilloscope data (this should be primarily determined by the thickness of green curve that is the oscilloscope wave).
    4. Determine whether Faraday's law is confirmed to within this uncertainty.

    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.]

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