The earth's magnetic field at the equator is approximately `0*4G`, Estimate the earth's dipole moment.

Explanation

From Eq (5.7), the equatorial magnetic field is `B_(E)=(mu_(0)m)/(4pi r^(3))`
We are given that `B_(E)-0.4G=4 xx 106(-5)T.` For r we take the radius of the earth `6.4 xx 10^(6) m`. Hence `m=(4 xx 10^(-5) xx (6.4 xx 10^(6))^(3))/(mu_(0)//4pi)=4 xx 10^(2) xx (6.4 xx 10^(6))^(3) (mu_(0)//4pi=10^(-7))`
`=1.05 xx 10^(23) Am^(2)`
This is close to the value of `8 xx 10^(22) A m^(2)` quoted in geomegnetic texts.