Question

Sketch four magnetic field lines as obtained in a limited space on a horizontal plane in the earth's magnetic field alone.

Answer 1

Hint: The horizontal plane is defined as the plane parallel to the ground. “In a limited space implies that the area considered is very small relative to the entire area of the earth. i.e. a very localised area.

Complete step by step answer
It is popularly mentioned that the earth is a giant bar magnet. This is because the earth’s magnetic field has its field lines very similar to that of a bar magnet. Hence, the earth is as though a giant magnet is placed at its centre.
As of any magnet, the magnetic field lines of the earth originate from the north and ends at the south. This particular north is known as the magnetic north and is actually oriented towards the geographic south. In general, the geographic north is about the same direction as the magnetic south and the geographic south is in the same direction as the magnetic north. Hence, the magnetic north of the seeming bar magnet between the earth is pointed downward. Hence the magnetic field lines of the earth points upward towards the magnetic south (geographic north).
In general, the magnetic field of the earth is as shown below

We see that from the diagram above, most of the field lines are parallel to the earth surface, hence, picking a horizontal plane (plane parallel to the earth surface) all field lines will go above or below at a localized area as shown (the horizontal plane is the plane of the paper or screen).

Note
We should also observe that although the lines are mostly parallel to most of the earth surface, they are not close to and at the north pole and south pole. As we move the poles, the magnetic field deviates from being horizontal and gradually towards the vertical. At zero degree magnetic, north pole or south pole, the magnetic field lines are vertical.