The lines of force due to the Earth's horizontal component of the magnetic field are:

If the dip circle is set at $45^{\circ}$ to the magnetic meridian,then the apparent dip is $30^{\circ}$. The true dip of the place is:

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

Let $V$ and $H$ be the vertical and horizontal components of the Earth's magnetic field at any point on Earth. Near the North Pole:

At some location on Earth,the horizontal component of Earth's magnetic field is $18 \times 10^{-6} \ T$. At this location,a magnetic needle of length $0.12 \ m$ and pole strength $1.8 \ A \ m$ is suspended from its mid-point using a thread. It makes a $45^{\circ}$ angle with the horizontal in equilibrium. To keep this needle horizontal,the vertical force that should be applied at one of its ends is:

The horizontal component of the earth's magnetic field at any place is $0.36 \times 10^{-4} \; Wb/m^2$. If the angle of dip at that place is $60^{\circ}$,then the value of the vertical component of the earth's magnetic field will be ........ $\times 10^{-4} \; Wb/m^2$.