Answer the question regarding earth's magnetism:
The earth's field, it is claimed, roughly approximates the field due to a dipole of magnetic moment `8 xx 10^(22) JT^(-1)` located at its centre. Check the order of magnitude of this number in some way.

Explanation

(e) Using formula `B_(e) = (mu_(0)) /(4pi ) ((m)/( r^3) )` and placing the values `m= 8 xx 10^(22) J//T` (or `Am^(2)), r=R_(e)=6.4 xx 10^(6)` m when we find out value of `B_(e)`, it comes out to be 0.3052 G (Gauss) which is quite close to experimentally measured value. This means that magnetic field of bar magnet with magnetic dipole moment `8 xx 10^(22) J//T`.