Explain the angle of dip.

(N/A) The angle of dip (or magnetic inclination) is the angle that the total magnetic field vector $\vec{B}_{E}$ of the Earth makes with the surface of the Earth (horizontal) at a given point.
If a magnetic needle is perfectly balanced about a horizontal axis so that it is free to rotate only in the vertical plane of the magnetic meridian,it will not remain horizontal but will tilt at an angle with the horizontal. This angle is known as the angle of dip $(I)$.
At the magnetic poles,the needle points vertically downward or upward,so the angle of dip is $90^{\circ}$. At the magnetic equator,the needle remains horizontal,so the angle of dip is $0^{\circ}$.
Figure $(b)$ shows the magnetic meridian plane at a point $P$ on the surface of the Earth,where $\vec{B}_{E}$ is the total magnetic field,$H_{E}$ is the horizontal component,and $Z_{E}$ is the vertical component of the Earth's magnetic field.