Question

 The earth’s field, it is claimed, roughly approximates the field due to a dipole of magnetic moment 8 × 10²² J T^-1 located at its centre. Check the order of magnitude of this number in some way.

Answer 1

Let us consider the magnetic field on surface of earth due to assumed bar magnet of dipole moment 8 × 10²² J T^-1 located at centre of earth. The magnetic field at point P equatorial position on earth can be calculated as