Magnetic Elements at a Place

Earth behaves as a magnet. The declination (α), the dip (δ), and the total intensity of earth’s magnetic field (B) are the three magnetic elements of earth’s magnetic field at a place. Declination gives the plane, dip gives the direction, and the intensity of magnetic field gives the magnitude of the earth’s magnetic field.

Magnetic elements of earth’s magnetic field.


(i)    Magnetic declination. The angle between magnetic meridian and geographical meridian at a place is called magnetic declination at that place. Its symbol is α.

ABEF is geographical meridian. ABCD is magnetic meridian. ∟FAD = α, is magnetic declination.

(ii)    The angle between the direction of the earth’s magnetic field and the horizontal direction at a place is called the angle of dip (or merely dip) (δ) at that place.

(iii)    Strength (intensity) of earth’s magnetic field. The strength (intensity) of earth’s magnetic field at a point in the field is defined as force acting on a unit north pole (test pole) kept at that pint in earth’s field. Its symbol is B.

Horizontal component of earth’s magnetic field.

The strength (intensity) of earth’s magnetic field at a point in the field is defined as force acting on a unit north pole (test pole) kept at that point in earth’s field. Its symbol is BH.

Hence, BH = B cos δ is along AD.
BH is sometimes taken as the third magnetic element in place of B.

Vertical components of earth’s magnetic field.

The component of total intensity of earth’s magnetic field at a point, taken in the vertical there, is called the vertical component of earth’s magnetic field. Its symbol is Bv.
    BV = B sin δ is along AB.
    Bv = BH = B sin δ/B cos δ = tan δ