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Homework Help: Electric Field Lab

  1. Jul 13, 2008 #1
    1. The problem statement, all variables and given/known data

    These questions are based on a laboratory measuring electric field in a two-dimensional deionized water tray using a 12 volt potential difference from a power supply. The positive electrode is on the right-hand side of the tray and the negative electrode is on the left hand side of the tray. The insulator or conductor are placed in the tray at separate instances closer to the positive electrode. The hoop is placed in the middle of the tray separately.

    A: How does the presence of the insulator affect the [electric] field lines? Why?

    B: How does the presence of the conductor affect the [electric] field lines? Why?

    C: How does the presence of a metal conducting hoop affect the electric field? Why?

    2. The attempt at a solution

    A: The insulating plastic bar caused all of the measured voltage lines (10V, 8V, 6V, 4V, 2V), but most notably the four volt and two volt lines to shift closer to the negative electrode. The ten volt line was "pulled" closer to the insulator and away from the positive electrode.

    Could this be due to a induced dipole created in the insulator? If there is a dipole in the insulator, would that cause the electric field lines to shift around it? How do electric fields react to insulators in general?

    B: The presence of a single conducting metal bar “pushed” the eight volt and ten volt lines closer to the positive electrode but the rest of electric field stayed the same. The presence of two conducting metal bars also caused a shift in the eight volt and ten volt lines, pushing them towards the positive electrode. The six volt line was found to be in the middle of the two bars.

    Although the metal bars conducted the charges, there were still shifts in the electric field. Could this be due to surface charges on the conductor that attract/repel the electric field around them? How do conductors placed in electric fields typically alter the field?

    C: The metal hoop caused the electric field to split around the hoop with the six volt line closer to the negative electrode and the eight volt line closer to the positive electrode. Only the six volt electric field was measured inside the hoop.

    It seems that the hoop caused all of the field lines to repel away from the outside surface and towards the electrodes. However, I'm baffled as to why the six volt was found inside the hoop?
  2. jcsd
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