Magnetic Field Strength at a Point Due to a Bar Magnet

Chapter-5|Magnetism and Matter| NCERT 12th Physics:

Magnetic Field Strength at a Point Due to a Bar Magnet:

The Strength of magnetic field at any point is defined as, the force experienced by a hypothetical unit north pole placed at that point. It is a vector quantity. The direction of magnetic field B is the direction along which hypothetical unit north pole would tend to move.

When Point Lies on Axial Line of a Bar Magnet:

Let 2l be the magnetic length of a bar magnet with centre O. The magnetic dipole moment of the magnet be M, where M= m×2l. Let OP= r, is the distance of the point P on the axial line from the centre of the magnet.

Magnetic Strength(force) at P due to South pole of the magnet is

When Point Lies on Equatorial Line of a Bar Magnet:

Let a bar magnet NS of length 2l and pole strength m. Let magnetic field is to be determined at a point P lying on the equatorial line of the magnet NS at a distance r from its centre.