Why is the electric field shaped this way?

  1. I did a lab where the where two electrodes are equidistant on a paper.
    on the picture the center line is 5 volts ,left electrode is 0 volts, with an outer electric fields of 3 volts. On the right side its 10 volts max ,with an outer circle field 7 V.

    I was wondering why the left side makes a rectangular semicircle like that. Is it because th right side has higher voltage?

    the lab is called Electric Fields and electric Potentials.
    sorry for the poorly drawn picture.
     

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  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,282
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    Please be careful with your descriptions. Imagine that the person you are talking to is on the other side of the World and has never seen your experiment setup.
    Equidistant to what? Do you mean the electrodes are centered on the paper?

    I'm guessing that the points are the electrodes.
    0V usually just means that you put the negative terminal of the voltmeter there, but it could mean that the electrode is physically grounded too. Which is it?

    Is the "outer field of 3V" the U shaped line about the left electrode position?
    Is the center line to line on the paper where you always get 5V?

    I don't know what this means. D you mean that the circle drawn around the right spot is 7V, and that the edge of the paper is maintained at 10V?

    The lines which are all the same voltage are called "equi-potential" lines.
    The electric field lines are always at right angles to them.

    You'll get an idea of why the equipotential lines are the form they are if you sketch in the electric field ... start with the field due to the electrodes.
     
  4. The 3V curve should close in a circle symmetrically to the 7V curve.
     
  5. Simon Bridge

    Simon Bridge 15,282
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    Given a certain set of assumptions.
    Either the experimenter has made a mistake in finding that curve or there is something else going on in the setup.
     
  6. For example, the wire with which the 0V-electrode was connected could be running 'to the left' right under the sheet of paper. Or something else which also has 0V-potential.
     
  7. Simon Bridge

    Simon Bridge 15,282
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    @Sneakertone: any of this any use?
    Cannot help you if you don't provide feedback.
     
  8. sorry I did not provide enough information or wasnt clear enough.
    but the picture creates a circuit where the power supple goes into the left side where the left pin is negative and comes out of the right making it positive.

    I found out that it makes the shape because of the charge on the pins since positive push outward and negative push inward. so everything on the left side goes to the left.
     
  9. sophiecentaur

    sophiecentaur 14,192
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    That odd shape on the left could be to do with the routing of the wires to those points, I think. If you bring the wires in normally to the surface and if they are reasonably long then you would expect circles.
    Or could there be an earthed clamp (or equivalent) under the paper on the left?

    BTW, I don't think it's been pointed out that your picture is, in fact, of Potential and not field. The field 'lines' would be normal to the equipotential lines you have drawn.
     
  10. Simon Bridge

    Simon Bridge 15,282
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    That does not make any sense.
    See: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/equipot.html

    [​IMG]

    Here you see two electrodes - one positive and one negative.
    The dotted red lines are the equipotentials that you were drawing (starting to draw).
    You got the circle around the (+) and the mirror line, but see how the negative is different to yours?

    The black lines are electric field - see how they relate to the equi-potentials?

    Post #2 - last three sentences :) But it bears repeating.
    I think you have the most likely cause of the odd potential.
     
  11. sophiecentaur

    sophiecentaur 14,192
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    I missed that, Simon but I thought it must be in there somewhere!
    The Field / Potential confusion is very common and is responsible for a lot of wrong conclusions. Those pictures of yours are very useful.
     
    Last edited: Feb 18, 2014
  12. you are correct. I compared data with someone else and the had about what you had on the picture . But they used a different scale with reading the volts and they measured other numbers in between to find the symmetrical shape
     
  13. Simon Bridge

    Simon Bridge 15,282
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    They used a different kind of voltmeter that was more sensitive?
    It would have been better for you to get more lines in - yes.
    Basically, either there was a wire touching the paper going to the negative electrode or you made a mistake.
    It happens.

    I want to stress: you didn't "get it wrong" - you got an unexpected result.
    The fact that you got something unexpected and are able to figure what it means is actually better than if you had got the expected result so don't feel bad: this is Good. You gained more from the lesson than those students who got the expected result. IRL: When odd stuff happens, that's where scientific discoveries lie.
    Enjoy.
     
  14. sophiecentaur

    sophiecentaur 14,192
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    If all experiments in Science gave the expected result, we wouldn't need to keep on experimenting. You got a strange result and you queried it. That was the right thing to do. A lesson from your experience is that it is always worth doing extra measurements in an area where results are unexpected. Unfortunately, lab time often gets in the way of chasing things like that.
     
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