Name three elements required to specify the earth's magnetic field at a given place. Draw a labelled diagram to define these elements. Explain briefly how these elements are determined to find out the magnetic field at a given place on the surface of Earth.
Solution
The three magnetic elements of the Earth at a place are: (i) Magnetic declination θ - the angle between the geographic meridian and the magnetic meridian. (ii) Angle of dip (inclination) δ - the angle Earth's total field B makes with the horizontal. (iii) Horizontal component BH - the horizontal part of Earth's field in the magnetic meridian. Declination is read as the angle between the compass needle's vertical plane and true north; the dip is read on a dip circle set in the magnetic meridian; BH is measured with a horizontal magnetometer. From these, the total field follows from
