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Ring of charge (half positive, half negative)

  1. Jan 27, 2013 #1
    1. The problem statement, all variables and given/known data

    Two half-rings of charge of opposite polarity are brought together at the origin (so that the rings create a full circle against the y- and z-axis. Each half-ring has a charge of magnitude Q and radius a. Derive the net electric field at point P, located on the +x axis a distance d from the centre of the two half-rings.

    2. Relevant equations

    Not sure.

    3. The attempt at a solution

    I really have no idea how to work this out from what we learned in lecture; "electric field of a ring of charge".. Help, please!
  2. jcsd
  3. Jan 28, 2013 #2


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    As start, can you figure out the direction of the field there? Let the line of join of the semicircles be the y-axis, say. Consider separately the components of the field in the x, y and z directions. Can you see any that must cancel by symmetry?
  4. Jan 28, 2013 #3
    I've worked it out conceptually to see that only those in the z direction do not cancel out but I'm at lost on how to retrieve that mathematically.
  5. Jan 28, 2013 #4


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    Explain to us how to find the field due to a ring of charge then — you know, what you went over in lecture. If you understand what was done there, you should be able to make a dent in this problem.
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