Engineering Physics I - Earth's Magnetism

 

Earth’s Magnetism

Our earth behaves as a powerful magnet whose south  pole is towards earth’s north pole and north pole towards the earth’s south pole. It is clear from following evidences (k|df0fx?+_ M

a.       A freely suspended magnetic needle stays in north-south direction.

b.      An iron piece buried in earth becomes magnet after a long time.

c.       Availability of neutral point.

Elements of earth’s magnetism:

There are three elements of earth’s magnetism. They are as follows:

a.     a.  Angle of declination

b.      b. Angle of dip

c.      c.  Horizontal component of earth’s magnetic field

a.     a.   Angle of declination

The acute angle between the magnetic meridian and the geographical meridian is called angle of declination.

Magnetic meridian:

The vertical plane passing through the axis of a magnetic needle suspended freely through its center of gravity is called magnetic meridian.

Geographical meridian:

The vertical plane passing through the line joining the geographical north and south  pole is called geographical meridian.

a.      b.  Angle of dip:

The angle between the axis of the needle in the magnetic meridian and the horizontal direction is called the angle of dip.

Actually the angle of dip at a place is the angle between the direction of earth’s magnetic field and the horizontal in magnetic meridian at that place.

In northern hemisphere (pQ/L uf]nf{4_, the north pole of the magnetic needle inclines downward.

In southern hemisphere (blIf0fL uf]nf{4_, the south pole of the magnetic needle inclines downward.

a.      c. Horizontal component of earth’s magnetic field

The earth’s magnetic field B_e in a magnetic meridian may be resolved into a horizontal component H and a vertical component V. Of these, the horizontal component H is more important from the experimental point of view.