For infinite length conductor and observation point is near the centre of the conductor ,
B = μ o / 4 π 2I / r
for infinite length conductor and observation point is near one end of the conductor ,
B = μ o / 4 π I / r
Magnetic Field Lines
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They are used to res present magnetic B field in a region . � They are closed continuous curves . � Tangent drawn at any point gives the direction of magnetic field . � They cannot interact . � Outside a magnet , they are directed from north to south pole and inside a magnet they are directed from south to north . �
The magnetic field lines due to a straight current carrying conductor are concentric circles having centre at conductor and in a plane perpendicular to the conductor .