Permanent magnets - Laws

Tangent law of perpendicular fields

External magnetic field B may be written in terms horizontal component of earth’s magnetic field B_H and deflection of compass needle θ.

B = B_H tan θ

Gauss’s law for magnetism

∫B.dS = µ₀*m_inside0

But m_inside0 is zero as we do not have an isolated magnetic pole in nature. The smallest unit of the source of magnetic field is a magnetic dipole where the net magnetic pole is zero.

Hence Gauss’s law for magnetism states that

∫B.dS = 0