If declination at a place is known to be $15^{\circ} \,E$. And a compass needle points as shown, then geographic north is represented by the direction numbered.

A short bar magnet is placed in the magnetic meridian of the earth with north pole pointing north . Neutral points are found at a distance of $30\, cm$ from the magnet on the East - West line, drawn through the middle point of the magnet. The magnetic moment of the magnet in $Am^2$ is close to: (Given $\frac{{{\mu _0}}}{{4\pi }}\, = 10^{- 7}$ in $SI\,units$ and $B_H\, =$ Horizontal component field $= 3.6\times10^{-5}\, tesla$)

Define geographic meridian. and Define magnetic meridian.

At magnetic poles of earth, angle of dip is.....$^o$

The angle between the magnetic meridian and geographical meridian is called

Assume the dipole model for earth’s magnetic field $\mathrm{B}$ which is given by

${{\rm{B}}_{\rm{v}}} = $ vertical component of magnetic field

$ = \frac{{{\mu _0}}}{{4\pi }}\frac{{2m\,\cos \theta }}{{{r^3}}}$

${{\rm{B}}_H} = $ Horizontal component of magnetic field

${{\rm{B}}_H} = \frac{{{\mu _0}}}{{4\pi }}\frac{{m\,\sin \theta }}{{{r^3}}}$

$\theta $ $= 90^{°}$ -latitude as measured from magnetic equator.

$(a)$ Find loci of points for which : dip angle is $ \pm $ $45^{°}$