The magnetic field of 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 Earth. At Mumbai, declination is nearly zero. 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 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 not 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`.