A dip needle lies initially in the magnetic meridian when it shows an angle of dip $\theta $ at a place. The dip circle is rotated through an angle $x$ in the horizontal plane and then it shows an angle of dip $\theta '$. Then $\frac{{\tan \theta '}}{{\tan \theta }}$ is

In the magnetic meridian of a certain place, the horizontal component of the earth’s magnetic field is $0.26\;G$ and the dip angle is $60^o$. What is the magnetic field of the earth at this location?

The true value of angle of dip at a place is $60^o$, the apparent dip in a plane inclined at an angle of $30^o$ with magnetic meridian is

Give information about Earth’s magnetism.
 

A bar magnet of length $14 \,cm$ is placed in the magnetic meridian with its north pole pointing towards the geographic north pole. A neutral point is obtained at a distance of $18\, cm$ from the center of the magnet. If $B _{ H }=0.4 \,G ,$ the magnetic moment of the magnet is $\left(1\, G =10^{-4} T \right)$

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 zero;