At which place does the Earth's magnetism become horizontal?

The angles of dip are $30^{\circ}$ and $45^{\circ}$ at two different places. The ratio of the horizontal components of the Earth's magnetic field at these places will be:

Consider the plane $S$ formed by the dipole axis and the axis of the Earth. Let $P$ be a point on the magnetic equator and in plane $S$. Let $Q$ be a point of intersection of the geographical and magnetic equators. Obtain the declination and dip angles at $P$ and $Q$.

The magnetic compass is not useful for navigation near the magnetic poles because

If ${\phi_1}$ and ${\phi_2}$ are the angles of dip observed in two vertical planes at right angles to each other and ${\phi}$ is the true angle of dip,then:

The line on the earth's surface joining the points where the magnetic field is horizontal is known as: