Explain geographic meridian and magnetic meridian.
$(i)$ Geographic meridian : Consider a point on the Earth's surface. At such a point, the direction of the longitude circle determines the geographic north-south direction, the line of longitude towards the north pole being the direction of true north.
Definition : The vertical plane containing the longitude circle and the axis of rotation of Earth is called the geographic meridian.
$(ii)$ Magnetic meridian (Definition): The vertical plane at a place on the Earth passes through the imaginary line joining the magnetic north and the south pole is called magnetic meridian.
Explain angle of dip.
The lines joining the places of the same horizontal intensity are known as
Dip angle in vertical plane at an angle ${\cos ^{ - 1}}\,\left( {\frac{1}{{\sqrt 2 }}} \right)$ from magnetic meridian is $60^o$, then actual dip at that place
The magnetic field of earth is due to
If the dip circle is set at $45^o$ to the magnetic meridian, then the apparent dip is $30^o$. The true dip. of the place is