a magnetic needle is freely suspended, the alignment of the magnet does not exactly lie along the geographic meridian as shown in Figure . . The angle between magnetic meridian at a point and geographical meridian is called the declination or magnetic declination ( D ). At higher latitudes, the declination is greater whereas near the equator, the declination is smaller.
In India, declination angle is very small and for Chennai, magnetic declination angle is – o 16ʹ (which is negative (west)). The angle subtended by the Earth’s total magnetic field B with the horizontal direction in the magnetic meridian is called dip or magnetic inclination ( I ) at that point (Figure . ). For Chennai, inclination angle is o 28ʹ.
The component of Earth’s magnetic field along the horizontal direction in the magnetic meridian is called horizontal component of Earth’s magnetic field, denoted by B H . Let B E be the net Earth’s magnetic field at any point on the surface of the Earth. B E can be resolved into two perpendicular components. Horizontal component B H = B E cos I ( .
) Vertical component B V = B E sin I ( . ) Dividing equation ( . ) and ( . ), we get Figure .
Inclination angle Horizontal