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Homework Help: Dipole (electrical) and Electric Field Concept

  1. May 14, 2008 #1
    Hi all, I'm kind of confused right now about some concepts.

    - Dipoles are essentially point charges of the same magnitude but different signs that are a certain distance away from each other, right?

    -In my textbook, they were calculating a charged particle that is on the dipole axis. They got an a E that is in the direction of z (as opposed to x/y). Why is the direction of the electric field at the point P (on the dipole axis) z? The charges of the dipole and the charge at P are all on x, y plane, unless I misunderstood something.

    -However, in earlier examples with charges on the same plane with other charges, the E they got was restricted in the x,y plane.

    Why is this so? Am I missing something?

    Thanks in advance!
  2. jcsd
  3. May 14, 2008 #2


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    Homework Helper
    Gold Member

    If the dipole axis is in the direction of z, then the field at a point on the axis will also point along the z direction. You can understand this using the principle of superposition. Work out what the field due to each charge will be and add them (vector addition).
  4. May 14, 2008 #3

    Doc Al

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    Staff: Mentor

    The dipole axis is a line going through both charges. If that axis is the z-axis, then the field at some point along the z-axis will be parallel to the z-axis. On the other hand, the field at some point on the x-y plane that bisects the dipole (assume the dipole is at z = 0) will also be parallel to the z-axis.

    (dx beat me too it!)
  5. May 14, 2008 #4
    Never mind, I misunderstood what the textbook was saying, thanks for the input though.
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