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Earth’s Magnetic Field (Terrestrial Magnetism)

As per the most established theory, it is due to the rotation of the earth where by the various charged ions present in the molten state in the core of the earth rotate and constitute a current.
  • The magnetic field of Earth is similar to one which would be obtained if a huge magnet is assumed to be buried deep inside the Earth at its center.
  • The axis of rotation of earth is called geographic axis and the points where it cuts the surface of earth are called geographical poles (NgSg). The circle on the Earth’s surface perpendicular to the geographical axis is called equator (Fig. 18).
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Fig. 18
  • A vertical plane passing through the geographical axis is called geographical meridian.
  • The axis of the huge magnet assumed to be lying inside the earth is called magnetic axis of the earth. The points where the magnetic axis cuts the surface of earth are called magnetic poles. The circle on the Earth’s surface perpendicular to the magnetic axis is called magnetic equator.
  • The magnetic axis and geographical axis do not coincide but they make an angle of 17.5° with each other.
  • The magnetic equator divides the Earth into two hemispheres. The hemisphere containing south polarity of earth’s magnetism is called northern hemisphere while the other, the southern hemisphere.
  • The magnetic field of Earth is not constant but changes irregularly from place to place on the surface of the earth and even at a given place it varies with time too.
  • The direction of Earth’s magnetic field is from S (geographical south) to N (geographical north).




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