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Homework Help: Question about wires connected in series .

  1. Aug 11, 2004 #1
    question about wires connected in series.....

    Hi everyone, i was wondering if anybody here can help me out on a homework problem. The question states:

    Two long straight wires are suspended vertically. The wires are connected in series, and a current froma battery is maintained in them. What happens to the wires? What happens if the battery is replaced by an a-c source?

    i seriously wouldn't have posted this question in a normal situation, but my group and I are totally stumped on this... any help is greatly appreciated.. thnx!

  2. jcsd
  3. Aug 11, 2004 #2
    I would place a guess that the reason that is giving you difficulty is because it is a rather vague description of the issue and prone to misinterpretation. I'm really not certain I know exactly what they mean.

    I can wager a good guess though.

    1) The wires are hanging, but they must be connected. I believe they are trying to suggest this connection while neglecting it for the sake of the problem. In other words, imagine a tiny, thin, nearly massless conducting string connecting the ends of the two wires. It wont keep them from swaying, but it does allow current to flow. This is just my interpretation. Another that works might be to say the ends of the wires are just brushing against something conductive, like a metal plate. Same result in either case.

    2) Here is what you need to do to answer the problem. Ask yourself what direction the current is moving in if they are in series. Then ask what effect the two wires can have on each other. (hint: The wires each produce a magnetic field. How does this magnetic field affect the moving charges in each wire?)

    3) Finally, would that effect still be there if the current were alternating? Would it change?

    Let me know if this helped a little, and which parts you need more clarification on.
  4. Aug 11, 2004 #3
    Hi, thnx for the help... my group and I knew that each wire produces a magnetic field, but we didnt know how the AC would affect it. I would imagine the current would flow from the positive terminal of the battery to the negative in the DC situation... however, in the AC, i am totally lost... ugh..... any more help?? hehe:).

  5. Aug 11, 2004 #4
    First, what did you decide happens in the DC case?

    In the DC case you have current coming down one side and back up the other. The currents are opposite each other. In the AC case, current will come down one side and up the other, then get weaker until it finally reverses,

    So in the AC case the currents are still opposite each other. You can still determine the magnetic field and the forces it has on the moving electrons in the AC case. You just have to consider three possibilities; when the current is going one direction, when it is going another, and the middle moment when it isn't traveling. Of course most AC current switches very fast (60 times a second) but you can still imagine.

    Hope that helped some, and interested in what you've decided.
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