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Need some checking on these Multiple choice questions

  1. Oct 26, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-10-26_16-38-11.png
    upload_2015-10-26_16-39-21.png
    upload_2015-10-26_16-40-27.png
    upload_2015-10-26_16-44-11.png

    upload_2015-10-26_16-50-7.png
    For #5, I added option E, it's the same as B, but the charges are switched around.
    2. Relevant equations


    3. The attempt at a solution


    1) Even though A and B look similar, B seems more accurate. The arrows in the corner of A don't seem to point directly to the corner.

    2) plugging in values for x and y, answer should be B

    3) D, the electric field is independent of the test charge.

    4) Most unsure with this one, but I think the answer is C because the bounds looks correct there.

    5) So I added option E, but option B is my answer.
    If I were to rank the dipoles from highest potential energy: B > E > A > C > D.
     
  2. jcsd
  3. Oct 26, 2015 #2

    mfb

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    Correct.
    Right, as long as the integrand doesn't include a shift (e. g. (x-d)2 in the denominator).
    How did you get that order? In particular, where is the difference between A and C, or D and E?
     
  4. Oct 26, 2015 #3
    I look at how far the negative charge is from the positive plate, as the distance increases, the potential increases. The same for positive charge from negative plate. Is the order wrong?
     
  5. Oct 26, 2015 #4

    mfb

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    How do you combine the two different things then?
    It is.
     
  6. Oct 26, 2015 #5
    can you specify what two different things?
     
  7. Oct 26, 2015 #6

    mfb

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    One.
    Two
     
  8. Oct 26, 2015 #7
    I don't know if my reasoning is correct, but for this case, that is what I used.
    For example, look at B and E, the midpoints of each dipole is at the same height from the positive plate but B's negative charge is higher than the negative charge of E.

    Again, I don't know the answer, I don't even know if my reasoning is right.
     
  9. Oct 26, 2015 #8
    I think of the positive plate as the floor, and the negative charge is a baseball. If the baseball is higher up in the air, the potential energy is higher. If the baseball is on the floor, PE is 0.
     
    Last edited: Oct 26, 2015
  10. Oct 27, 2015 #9
    Ok, after doing more reading on dipoles.

    the order should be B>D> A=C

    and E probably is between B and D? I'm not sure.
     
  11. Oct 27, 2015 #10

    mfb

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    A=C is right.
    Why D>A?

    Your explanation is missing something, so I don't know where the error is.
    "I compare two persons by body height and by weight, and then rank them on a single scale" - how do you combine the two measurements to a single ranking system?
     
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