Magnetic Elements of Earth:
Magnetic Elements of Earth at a place are the quantities which describe completely in magnitude and in direction, the magnetic field of earth at that place.
Following are three Magnetic Elements of Earth:
- Magnetic Declination (θ).
- Magnetic Dip (δ).
- Horizontal Component (H).
The line joining the North and South poles of a freely suspended magnet is called magnetic axis whereas the line joining the geographic North and geographic South direction is called geographic axis.
Magnetic declination (θ) at a place is defined as the angle between the magnetic axis and geographic axis at that place.
A vertical plane passing through the N-S line of the magnet is called a magnetic meridian whereas the vertical plane passing through geographic North and geographic South is called a geographic meridian.
Magnetic declination (θ) at a place is also defined as the angle between magnetic meridian and geographic meridian. The value of magnetic declination at a place is approximately 20°.
It is defined as the angle between total strength of earth’s magnetic field and the horizontal line in magnetic meridian. It is denoted by δ. The value of DIP at a place lies between 0° and 90°. The value of DIP is 90° at poles and 0° at equator.
It is defined as the component of total strength of earth’s magnetic field in the horizontal direction.
In the given figure, ABCD is the magnetic meridian and AB’C’D is the geographic meridian.
∠B’AB = ∠θ is the magnetic declination whereas ∠BAK = ∠δ is the magnetic dip at a place.
|Now, Horizontal Component (H) is given by|
H = AL = R Cos δ ……….(i)
And, Vertical Component (V) is given by
V = AM = R Sin δ ……….(ii)
Square and add (i) and (ii), we have
H2 + V2 = R2 Cos2 δ + R2 Sin2 δ
⇒ H2 + V2 = R2 (Cos2 δ + Sin2 δ)
⇒ H2 + V2 = R2
⇒ R = √(H2 + V2)
Divide (ii) by (i), we have
V/H = R Sin δ/R Cos δ
⇒ V/H = tan δ
Note: The value of H at a place on the surface of the earth ≅ 3.2 x 10-5 Tesla.