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Shape of electromagnetic field around a straight wire carrying a current.

  1. May 18, 2005 #1
    This is an experiment which might prove interesting. We know , thanks to the work of Oersted and Ampere , that the field around a wire carrying a current and the field around a permanent magnet are identical. Both of these fields are caused by moving charges , although the field around a wire is thought to be due to the oscillation of ions in the crystalline lattice structure of the wire carrying a current , while the field around a permanent magnet is attributed to the alignment of spin of the electrons within the substance of the magnet. It is well known that a permanent bar magnet when suspended by a string will align itself in the direction of the earth’s magnetic field . What I wish to know is how would a wire carrying a current , align itself when suspended in a similar manner , would the wire align itself in the direction of the earth’s magnetic field or would it align itself differently. The experiment can be performed as follows. A straight wire is suspended horizontally from a string and a beam of electrons from an electron gun is directed at it in such a manner that the electrons impinge on one end of the suspended wire , causing a current to flow in the wire. It is possible that some sort of tracking device would be necessary in order to ensure that the current flows in the wire for a sufficient time in order for the wire to align itself. If the wire , when a current is flowing through it , aligns itself in the direction of the earth’s magnetic field , does it demonstrate that the field around a wire carrying a current and the field around a bar magnet are identical (i.e solenoidal ) fields.
    As a corollary to this , it follows that all electrical wires carrying an electrical current result in solenoidal (closed) fields ,since the current is essentially flowing between the two poles of a dipole , i.e between the positive and negative poles.
     
  2. jcsd
  3. May 18, 2005 #2

    Doc Al

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    Staff: Mentor

    Oh, really?
    :yuck:
     
  4. May 20, 2005 #3
    In continuation of this thread , it has occurred to me that a simpler way of determining the direction in which a free standing wire would orient itself if a current were flowing through it , would be to simply suspend the wire by a string , horizontal to the ground , making sure that it was aligned East to West or vice versa and then to move the wire laterally. Moving the wire laterally would result in the earth’s electromagnetic field inducing a current in it , the wire should then align itself in a north south direction just as a free standing bar magnet would. This leads to the thought that in a normal wire carrying a current , the current always flows as part of a circuit. Thus there are two solenoidal fields one from the current flowing between the negative and positive poles of the wire and the other flowing between the positive and negative poles of the EMF source. Since these two currents are flowing in opposite direction they interact by attracting each other. Could this be the reason why , in a wire carrying a current the field appears to manifest itself at right angles to the wire and therefore does not resemble the solenoidal field around a bar magnet ?
     
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