Differentiate between magnetic meridian and geographical meridian.

The elements of earth's magnetic field at a place are declination, dip and horizontal intensity.

A magnetic needle free to move in horizontal plane is shown below:

Which elements of earth's magnetic field is represented by $\mathrm{\theta }$ in the figure?

Where on the surface of the earth is the vertical component of earth's magnetic field zero?

The elements of earth's magnetic field at a place are declination, dip and horizontal intensity.

The vertical component of earth's magnetic field at a given place is $\sqrt{3}$ times its horizontal component. If total intensity of earth's magnetic field at the place is $0.4 \mathrm{G}$, find the value of horizontal component of earth's magnetic field.