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Magnetic field using Biot-Savart's Law

  1. Mar 13, 2014 #1
    1. The problem statement, all variables and given/known data

    An in finitely long hollow cylinder of radius a carries a constant current I. Use Biot-Savart's law
    and show that the magnetic field at the centre of the cylinder is zero.

    2. Relevant equations

    Biot-Savart's law

    3. The attempt at a solution

    I cannot seem to come up with anything meaningful. I have tried searching this question but it seems the best way is normally to use Ampere's law and not Biot-Savarts law. Could someone explain the steps or show the steps how we could use Biot-Savart's law in this case.
     
  2. jcsd
  3. Mar 13, 2014 #2
    This is really just a symmetry argument. Think about sitting between two wires that have current flowing in the same direction. You know the magnetic field from one wire (using the Biot-Savart law), and you know it is going to cancel that of the other wire in the middle. Now just line the surface of a cylinder with an infinite number of these wires and you have your problem, but you get the same result.
     
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