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
� � � �
� � � � �
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.