Question

The magnetic moment of the assumed dipole at the earth's centre is 8.0 × 10²² A m². Calculate the magnetic field B at the geomagnetic poles of the earth. Radius of the earth is 6400 km.

Answer 1

Given :
Magnetic moment of dipole at Earth's centre, M = `8.0 xx 10^22 "Am"^2`

Radius of Earth, `d = 6400  "km"`

The geomagnetic pole is at the end of the position (axial) of Earth.
Thus, the magnetic field at the axial point of the dipole (B) is given by 

`B = (u_0)/(4pi) (2M)/d^3`

⇒ `B = (10^-7 xx 2 xx 8 xx 10^22)/((64)^3 xx 10^15)`

⇒ `B = 6 xx 10^-5  "T" = 60  "uT"`