You have seen that a freely suspended or pivoted magnet comes to rest along the north-south direction. Experiments have shown that the earth behaves as a magnetized sphere. The strength of the earth's magnetic field varies from place to place on the earth's surface. Its value being of the order of 10 raised to -5 T.
The earths magnetic field was thought of as arising from a giant bar magnet approximately along the axis of rotation of the earth and deep in the interior. But this is certainly not correct. The magnetic field is now thought to arise due to electrical currents produced by convective motion of metallic fluids (consisting mostly of molten iron and nickel) in the outer core of the earth. This is known as dynamo effect.
The magnetic field lines of the earth resemble that of a (hypothetical) magnetic dipole located at the center of the earth. The axis of the dipoles does not coincide with the axis of rotation of the earth but is presently titled by approximately 11.3 degree with respect to the latter.
The location of the north magnetic pole is at a latitude of 79.74 degree N and a longitude of 71.8 degree W, a place somewhere in north Canada. The magnetic south pole is at 79.74 degree S, 108.22 degree E in the Antarctica. The magnetic poles are approximately 2000 km away from the geographic poles. The magnetic equator intersects the geographic equator at longitudes 6 degree W and 174 degree E, respectively.
The pole near the geographic north pole of the earth is called the north magnetic pole. Likewise, the pole near the geographic south pole is called the south magnetic pole. Since we know that unlike poles attract, the south pole of earth magnet is near the geographic north pole and vice versa.
Over small regions of space we can consider earth's magnetic field as uniform. So when a magnet is freely suspended in this uniform magnetic field it experiences a torque and aligns itself in the earth's field.
The earths magnetic field was thought of as arising from a giant bar magnet approximately along the axis of rotation of the earth and deep in the interior. But this is certainly not correct. The magnetic field is now thought to arise due to electrical currents produced by convective motion of metallic fluids (consisting mostly of molten iron and nickel) in the outer core of the earth. This is known as dynamo effect.
The magnetic field lines of the earth resemble that of a (hypothetical) magnetic dipole located at the center of the earth. The axis of the dipoles does not coincide with the axis of rotation of the earth but is presently titled by approximately 11.3 degree with respect to the latter.
The location of the north magnetic pole is at a latitude of 79.74 degree N and a longitude of 71.8 degree W, a place somewhere in north Canada. The magnetic south pole is at 79.74 degree S, 108.22 degree E in the Antarctica. The magnetic poles are approximately 2000 km away from the geographic poles. The magnetic equator intersects the geographic equator at longitudes 6 degree W and 174 degree E, respectively.
The pole near the geographic north pole of the earth is called the north magnetic pole. Likewise, the pole near the geographic south pole is called the south magnetic pole. Since we know that unlike poles attract, the south pole of earth magnet is near the geographic north pole and vice versa.
Over small regions of space we can consider earth's magnetic field as uniform. So when a magnet is freely suspended in this uniform magnetic field it experiences a torque and aligns itself in the earth's field.
Elements of Earth's Magnetic Field
Consider a point P on the earth's surface. At this point, the longitude determines the north-south direction. The vertical plane containing the vertical axis and the longitude is called the geographic meridian.
At P, there also exists the earth's magnetic field Be. The magnetic meridian is the vertical plane containing the earth's magnetic field Be and the vertical axis.
The angle between the geographic and the magnetic meridian planes is called the magnetic derivation. Declination is greater at higher latitudes and smaller near the equator.
If a magnetic needle is perfectly balanced, about a horizontal axis is so that it can swing in a plane of the magnetic meridian, the needle would make an angle with the horizontal. Thus dip is the angle that the total magnetic field of the earth makes with the surface of the earth.
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