The direction of magnetic field at any location on the earth's surface

The direction of magnetic field at any location on the earth’s surface is commonly specified in terms of

[amp_mcq option1=”field declination” option2=”field inclination” option3=”both field declination and field inclination” option4=”horizontal component of the field” correct=”option3″]

This question was previously asked in

UPSC CDS-2 – 2018

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The direction of the Earth’s magnetic field at any location is specified in terms of both field declination and field inclination.

The Earth’s magnetic field at a given point is a vector quantity with both magnitude and direction. To fully describe the direction of this vector in three-dimensional space relative to the Earth’s surface and geographic north, two angles are needed.
Magnetic Declination is the angle in the horizontal plane between magnetic north (the direction a compass needle points) and true geographic north.
Magnetic Inclination (or Dip angle) is the angle between the magnetic field vector and the horizontal plane. This angle measures how steeply the field lines dip into the Earth.
Together, declination specifies the horizontal direction (azimuth), and inclination specifies the vertical angle (dip), thus defining the orientation of the magnetic field vector.

The magnitude of the Earth’s magnetic field is also important, along with its direction. The horizontal component of the field is related to both the total field strength and the inclination (Horizontal Component = Total Field * cos(Inclination)). While the horizontal component is a part of the description, specifying the *direction* requires both declination and inclination.

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