4 Earth_s Magnetism
Earth’s Magnetism
Earth’s Magnetism
- Dynamo effect − The magnetic field of earth has arisen due to electrical currents produced by convective motion of metallic fluids in the outer core of the earth. This is known as the dynamo effect.
- The magnetic field lines of the earth resemble that of a magnetic dipole located at the centre of the earth. The axis of the dipole is presently tilted by approximately 11.3° with respect to the axis of rotation of earth.
- The North magnetic pole is located at latitude of 79.74° N and a longitude of 71.8° W, a place somewhere in North Canada. The magnetic South Pole is at 79.74° S and 108.22° E in Antarctica.
The pole near the geographic North Pole of the earth is called the North magnetic pole and the pole near the geographic South Pole is called the South magnetic pole.
- Geographic meridian − The vertical plane passing through the geographic North −South direction is called geographic meridian.
- Magnetic Meridian − The vertical plane passing through N − S line of a freely suspended magnet is called magnetic meridian.
Magnetic Declination and Dip (Or Magnetic Elements)
- Magnetic elements− The physical quantities, which determine the intensity of earth’s total magnetic field completely (both in magnitude and direction), are called magnetic elements.
- There are three magnetic elements of earth:
- Magnetic declination− Declination at a place is the angle between the geographic meridian and magnetic meridian. It is denoted by θ.
- Magnetic inclination or dip− Dip at a place is defined as the angle made by the direction of the earth’s total magnetic field with the horizontal direction. It is denoted by δ.
- Horizontal component of earth’s magnetic field− It is the component of earth’s magnetic field along the horizontal direction. It is denoted by BH.
In the figure, for right-angled triangle ALP,
BH = B cosδ … (i)
Also,
BV = B sinδ … (ii)
Squaring and adding the equations (i) and (ii), we obtain
Dividing equation (ii) by (i), we obtain
