The magnetic field of the earth can be modelled by that of a point dipole placed at the centre of the earth. The dipole axis makes an angle of 11.`3^(@)` with the axis of the earth. At mumbai, declination is nearlyzero, then.

Options

A. The declination varies between `11.3^(@)W " to " 11.3^(@)E`
B. The least declination is `0^(@)`
C. The plane defined by dipole axis and the earth axis passes through Greenwich
D. Declination averaged over the earth must be always negative

Answer

A

Explanation

For the earth’s magnetism, the magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth. The axis of the dipole does no coincide with the axis of rotation of the earth but is presently tilted by approximately `11.3^(@)` with respect to the later. This results into two situations as given in the figure ahead.

Hence, the declination varies between `11.3^(@)W " to " 11.3^(@)E`