Define magnetic lines of force and state its two properties.

Hint: You can distribute iron dust on a piece of paper homogeneously. Keep a permanent magnet on the paper and start tappy on the paper slowly. You will see the iron dust forming lines outside the magnet. These are the magnetic lines of force.

Complete step by step answer:

The definition of magnetic lines of force is -

“Magnetic lines of force are the lines that depict the magnetic force that exists in the surrounding of the magnet.”

Let’s look at the following diagram to understand magnetic lines of force.


The dotted lines are the magnetic lines of force outside the magnet and the solid arrows are the magnetic lines of force inside the magnet.

These lines show the presence of magnetic fields outside the magnet. The strength of the magnetic lines is the same throughout and is proportional to how close the lines are. We can find the magnetic field strength from the density of these magnetic lines.

These are two of the important properties of magnetic lines of force:

(a) Magnetic field lines originate from the north pole and end at the south pole. However, magnetic field lines inside the magnet start at the south pole and end at the north pole. Hence, the magnetic field lines complete a loop.

(b) As we increase the distance between the poles, the density of magnetic lines decreases. The magnetic field strength depends on the density of the magnetic field lines. We can find the magnetic flux, and in turn, find the magnetic field strength. We can consider the magnet as a magnetic dipole with its north pole and south pole separated by a certain distance. As we make the distance more, the magnetic field at a certain point also decreases.

Note: Another important property of magnetic lines of force is that the magnetic lines do not intersect at any point in space. The magnetic dipole creates non-intersecting sets of magnetic field lines around the magnet. Magnetic field lines cannot intersect because the magnetic field has to show a specific direction.