Thursday, November 8

Magnetic Field of the Earth

Introduction to Magnetic field of earth

Sir William gilbert was the first to suggest in year 1600, that earth itself is a huge magnet. His statement was based on the following evidence:

I. A magnet suspended from a thread and free to rotate in the horizontal plane comes to rest along the north-south direction. On disturbing, the magnet returns quickly to its north-south direction. This is as if a huge magnet lies along the diameter of earth. The north pole of this fictitious magnet must be towards geographical south so as to attract south pole of the suspended magnet and vice-versa.

II.When a soft iron piece is buried under earth’s surface in the north south direction, it is found to acquire the properties of a magnet after some time.I like to share this Magnets Rare Earth with you all through my article.

III.When we draw field lines of a magnet, we come  across neutral points. At these points, magnetic field due to the magnet is neutralized or cancelled exactly by the magnetic field of earth. If earth has no magnetism of its own, we would never observe neutral points.

Cause of Magnetic Field of the Earth

The exact cause of earth magnetism is not yet known. However, some important postulates in this respect are as follows:

a) According to Prof. Brackett, earth’s magnetism may be due to rotation of about its axis. This is because every substance is made up of charged particles. Therefore, a substance rotating about its axis is equivalent to circulating currents, which are responsible for the magnetization.

b)In the outer layers of the earth’s atmosphere, gases are in the ionized state, primarily on account of cosmic rays. As earth rotates, strong electric currents are setup due to movement of ions. These currents might be magnetizing the earth.Is this topic Transverse Waves and Longitudinal Waves hard for you? Watch out for my coming posts.

c)The earth’s core is very hot and molten. Circulating ions in the highly conducting liquid region of the earth’s core could form current loops and produce a magnetic field.

General Features of Earth’s Magnetic Field

It has been established that earth’s magnetic field is fairly uniform. The strength of this magnetic field at the surface of earth is approximately 10-4 tesla or 1 gauss. The field is not confined only to earth’s surface, it extends upto a height nearly 5 times the radius of earth.  At present the south pole of earth is located at a place on north Canada, longitude 960 W and latitude 70.50 N and the north pole is located diametrically opposite the south pole i.e. at longitude 840 E and latitude 70.50 S. The magnetic poles are approximately 2000 km away from geographic poles.

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