Magnetic Fields inside a conductor obey Ampere's Law. To find the field at any point inside a long, wire conductor you have to do a closed integral of **B **dl = U i, where **B** is the magnetic field, U is the permeability constant and i is the current. ...

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Magnetic Fields inside a conductor obey Ampere's Law. To find the field at any point inside a long, wire conductor you have to do a closed integral of **B **dl = U i, where **B** is the magnetic field, U is the permeability constant and i is the current. The result of the integration gives you

2XPiXrXB = UI(r^2/R^2) where I is the current at the surface of the wire, r is the distance from the center of the wire to the point of interest inside the wire, and R is the radius of the wire.

So B = UIr/2PiR^2. From this, we can see that when r approaches zero (the center of the wire), B = 0.