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Magnetic field outside a wire coiled on an iron cyl.

  1. Mar 19, 2013 #1
    If we consider the common electromagnet that is made by passing current through a wire coiled around an iron core, I wonder what effect produces more magnetic field:

    1. The field produced outside the solenoid due to the current in the wire
    2. For this effect I dont insist that the object is iron or even ferromagnetic, just capable of having a net magnetism induced (ie: electron spin aligned along the axis of the solenoid in the direction of the field, paramagnetism i believe). This alignment produces an external magnetic field.

    My question is which effect dominates and provides the larger contribution to the total magnetic field outside?
    I hope the question is clear.

    Thank you,
  2. jcsd
  3. Mar 20, 2013 #2
    Well just as you said current in wire creates an electromagnetic field , now it would be sufficient with the wire wrapped in a coil alone to make the field , iron cores are used just to make the whole device many times more efficient and powerful.

    Now right you said that the wore around the iron of ferromagnetic core make the electrons in the iron align and produce a net magnetic field , the iron become a magnet.
    Now let's be clear without the current going in the wire there would be no field outside so I can't say that iron is responsible for the field , the field is there because of the flow of charge through a conductor in the first place , iron is just a material assisting in this creating the magnetic field stronger and more focused.(depends on the shape of the iron core)
    It is hard to say what makes a bigger contribution to the field outside , rather the flow of current makes one and the iron just adds o the sum.

    By the way you don't always need a core to make the electromagnetic field going good.Cores are needed where lower frequencies of the em spectrum are used like in power electromagnets or transformers. (electromagnets can also come with dc where there is no frequency)
    Using higher frequencies you can have the field pretty string even without the addition of an iron core like some high frequency coreless transformers where two special field coils are placed near each other and the high frequency em field induces current in the secondary winding.Radio transmission works similarly too.
    Also going in higher frequencies makes the iron pretty bad because alot of the energy is lost as heat.So there is a limit to how high iron/ferrite materials can go.
    Last edited: Mar 20, 2013
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