Final answer:
Magnetic field lines originate from a magnet's north pole, curve around in space, and enter into its south pole, thus forming closed loops. These lines help visualize magnetic field direction and strength, where a high line density indicates a stronger field. Magnets always have both a north and a south pole and do not exist as isolated monopoles.
Step-by-step explanation:
Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole. This behavior illustrates an important concept in magnetism where the field lines emanate from the north pole, curve through space, and then sink into the south pole, forming continuous loops. It is a fundamental principle of magnetism that these lines never cross and always form closed loops, clearly demonstrating the dipolar nature of magnetic fields. Moreover, the field lines are a useful way to visualize the direction and strength of the magnetic field, with the density of the lines indicating the intensity of the field.
All magnets, irrespective of size or shape, have both a north pole and a south pole as seen in Figure 22.3. According to this fundamental property of magnetism, there is never an isolated monopole. An interesting real-world application of magnetic fields is that charged particles, like cosmic rays, can spiral along these field lines, and this principle leads to phenomena such as the Aurora Australis or Aurora Borealis, where the energized particles cause the atmospheric gases to glow when they strike the Earth's magnetic poles.