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The direction "magnetic north" at a position on the Earth is the…

  • A
    compass North at that position corrected for variation.
  • B
    great circle between the position and the magnetic North Pole.
  • C
    direction of the horizontal component of the Earth’s magnetic field at that position.
  • D
    isogonal to the magnetic North Pole.

Refer to figure.
HORIZONTAL COMPONENT
A freely suspended magnet will align itself with the Earth's magnetic field. The total field (T) is resolved into a horizontal component (H) and a vertical component (Z). The horizontal component is the part which is detected by the compass needle in order to determine Magnetic North. The compass’ needle will align itself with the Earth's horizontal component (H) of the Earth's magnetic field.

  • The compass is ineffective near the poles. As you approach the poles, the angle between magnetic flux and the horizon becomes vertical – compass ‘dip’ becomes a factor => decrease in horizontal magnetic field, increase in vertical magnetic field.
  • The value of the horizontal component is maximum at the Magnetic Equator, a freely suspended compass needle in the Earth's magnetic field will be horizontal to the Earth - in line with the horizontal component.

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