A freely suspended magnetic needle at a point on Earth comes to rest approximately along the geographical north-south direction. This shows that the Earth behaves like a huge magnetic dipole with its magnetic poles near its geographical poles. Since the north pole of the magnetic needle approximately points towards the geographic north (NG) it is appropriate to call the magnetic pole near NG as the magnetic south pole of Earth Sm. Also, the pole near SG is the magnetic north pole of the Earth (Nm). (Figure)
The Earth’s magnetic field at any point on the Earth can be completely defined in terms of certain quantities called magnetic elements of the Earth, namely
(i) Declination or the magnetic variation θ.
(ii) Dip or inclination δ and
(iii) The horizontal component of the Earth’s magnetic field Bh.