Hi,(adsbygoogle = window.adsbygoogle || []).push({});

I studied the Maxwell laws and the Biot Savart law and I found something I cannot answer.

If you have a finite wire carrying current (let say 5m long) and you want to determine the magnetic induction vector due to it at some point that has distance r from the wire, you have 2 options I think.

If you use the Biot Savart law and you integrate over the lenght of the wire you get an answer which is definitely less than the answer you would get if the wire would be infinite.(B=µ_{0}*I/(2*r*), where B is the magnetic induction vector, I is the current of the wire and r is the distance from the wire)

However if you use Ampere's law for a circle around the wire (the wire is at the center of the circle and the plane of the circle is perpendicular to the line of the wire) you get that the magnetic field is B=µ_{0}*I/(2*r*) since there is only the current I crossing the circle and there is no change in flux. It is the same as the magnetic field generated by an infinite long wire. So that is definitely bigger than u get from the Biot Savart law.

I can't figure out why the 2 methods don't give the same result so if you could help me out please do so. It would be really appreciated.

Thanks,

Istvan

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# I Magnetic field created by a current carrying wire

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