The magnetic field at a point on the magnetic equator is found to be `3.1 xx 10^(-5) T`. Taking the earth's radius to be 6400 km, calculate the magneitc moment of the assumed dipole at the earth's centre.

Explanation

A point on the magnetic equator is in broadside-on position of the earth's assumed dipole (figure). The filed is, therefore,
`B = (mu_0)/(4pi) M/R^3`
or,
M = (4pi)/(mu_0) BR^3`
`= 10^7 A m^(-1) xx 3.1 xx 10^(-5) T xx (6400 xx 10^3)^3 m^3`
`8.1 xx 10^22 A m^2`.