The earth's field, it is claimed, roughly approximates the field due to a dipole of magnetic moment `8xx10^(22)JT^-1` located at its centre. Check the order of magnitude of this number in some way.

Answer

Checked and found correct

Explanation

Here, `M=8xx10^(22)T^-1`
Radius of earth, `R=6400km=6*4xx10^6m`.
Magnetic field strength at any point on surface of earth on the right bisector of dipole is
`B=(mu_0)/(4pi)M/d^3=(10^-7xx8xx10^(22))/((6*4xx10^6)^3)=0*305xx10^-4T`
`B=0*305 gauss`
which is the usual value of horizontal component [H] of earth's field, we use.