The earth’s magnetic field at the equator is approximately $0.4 \;G$. Estimate the earth’s dipole moment.
the equatorial magnetic field is,
$B_{E}=\frac{\mu_{0} m}{4 \pi r^{3}}$
We are given that $B_{E} \sim 0.4 G =4 \times 10^{-5} T .$
For $r,$ we take the radius of the earth $6.4 \times 10^{6} m .$ Hence,
$m=\frac{4 \times 10^{-5} \times\left(6.4 \times 10^{6}\right)^{3}}{\mu_{0} / 4 \pi}$$=4 \times 10^{2} \times\left(6.4 \times 10^{6}\right)^{3} \;\;\left(\mu_{0} / 4 \pi=10^{-7}\right)$
$=1.05 \times 10^{23} Am ^{2}$
This is close to the value $8 \times 10^{22}\; A m ^{2}$ quoted in geomagnetic texts.
Give the location of magnetic :
$(i)$ north pole
$(ii)$ south pole
Points $A$ and $B$ are situated perpendicular to the axis of a small bar magnet at large distances $x$ and $3 x$ from its centre on opposite sides. The ratio of the magnetic fields at $A$ and $B$ will be approximately equal to
Earth magnetic field at equator is approximately $0.4\,G$ then earth's dipole moment would be (nearly) (ralius of earth $= 6.4 \times 10^6\,m$ )
The net magnetic flux through any closed surface is
Assertion : The poles of magnet can not be separated by breaking into two pieces.
Reason : The magnetic moment will be reduced to half when a magnet is broken into two equal pieces.