## 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).

### Magnetic Declination:

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°.

### Magnetic Dip:

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.

### Horizontal Component:

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 H ^{2} + V^{2} = R^{2 } Cos^{2} δ + R^{2 } Sin^{2} δ⇒ H ^{2} + V^{2} = R^{2} (Cos^{2} δ + Sin^{2} δ)⇒ H ^{2} + V^{2} = R^{2}⇒ R = √(H ^{2} + V^{2})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. |