Question

What are magnetic field lines? How is the direction of the magnetic field at a point in a magnetic field determined using field lines?

Answer 1

Hint: The magnetic field around a magnet can be visualised by drawing hypothetical lines originating from the magnet's north pole and ending at the magnet's south pole. They basically tell the direction of the magnetic field at a point.

Complete step by step answer:
A magnetic material like a bar magnet exhibits a magnetic field around itself. The magnet has a north pole and a south pole. This field can be visualized in front of lines originating from the north pole of the magnet and ending at the south pole. These hypothetical lines are called magnetic field lines.

The magnetic field lines never intersect each other and give information about the intensity and direction of the magnetic field at a point. Denser the magnetic field lines, greater is the strength of magnetic field at those points.
The direction of the magnetic field at a point can be determined using magnetic field lines. The lines are directed from north pole to the south pole outside the magnet while they are directed from south pole to north pole inside the magnet. A tangent drawn on a magnetic field line gives the direction of the magnetic field at that point. The direction can also be determined by using a magnetic compass. When a magnetic compass is placed on a magnetic field line, then it always points in the direction of the magnetic field at that point.

Note: There cannot exist an isolated north pole or south pole. When magnetic lines of force originate from a north pole they must end at a south pole. Unlike magnets, isolated charges can exist, but a magnetic monopole does not exist in nature.