Magnetic north pole and south pole
What is meant by magnetic north pole and south pole?
The north pole and south pole are the two different poles of a permanent magnet. The magnetic field originates at the north pole and runs to the south pole, as can be shown by field lines. The field lines then close again inside the magnet. Like poles repel each other (i.e. north pole against north pole or south pole against south pole), whereas opposite poles attract each other. The magnetic force acting on a ferromagnetic material (e.g. iron) is attractive at both the north pole and the south pole.Table of Contents
Every magnet has two poles.
This is a fundamental property that distinguishes electric fields and magnetic fields.
A magnetic field is created when a current flows. Or in other words, whenever electrical charges are in motion. In this case, however, the created field will always have two poles, i.e. a north pole and a south pole. This is why it is also referred to as a dipole field. It is similar to the electric field of two opposite charges, the electric dipole.
In a permanent magnet, i.e. in a magnetised material, there are also elementary electron spins with a magnetic moment, which can be understood as elementary magnets. The macroscopic magnetic field of the permanent magnet is the sum of the contributors of all elementary magnets. The electron spins have the same effect as atomic circular currents, and each has a magnetic north and south pole.
While an electric charge, e.g. a negatively charged electron, causes an electric field, there is no single "magnetic charge". It is not possible to produce a single magnetic pole.
It is said that the electric field has sources (namely the electric charge), and the magnetic field, on the other hand, is source-free. It emerges as a dipole field (with a north and a south pole) when electric charges are in motion. There is no real proof that the magnetic field is source-free, but to date, nobody has observed a "magnetic charge" either.
However, Maxwell's equations can be used to mathematically prove that there are no individual magnetic poles. But, to do so, one has to accept Maxwell's equations, as their validity itself cannot be proven.
Each magnet has a north pole (N) and a south pole (S).
If you break a permanent magnet, you end up with two smaller magnets, each of which also has a north pole and a south pole.
This can be understood due to the fact that a magnetic field is created by aligned electron spins in the material.
Like tiny circular currents in the material, these have a magnetic moment and cause a north pole and a south pole at each point, whose forces overlap to form the macroscopic magnetic field.
Attraction and repulsion of the magnetic poles
If the north pole of a rod magnet is brought close to the north pole of another magnet, both magnets repel each other. If, on the other hand, the south pole of a rod magnet is brought close to the north pole of another magnet, the force between the magnets has an attractive effect.To test this assertion, you only need to hold one end of a magnet in your hand, and you will notice that the free end is always attracted to one side of another magnet but repelled by the other side of said magnet.
Thus, repulsive forces always act between like poles of different magnets (i.e.
between north pole and north pole or between south pole and south pole).
Attractive forces, on the other hand, act between unlike poles of different magnets (i.e.
between the north pole and south pole).
The magnetic field gives an idea of the force exerted by a magnet. In physics, the strength of a magnetic field is usually indicated by the magnetic flux density B and is measured in the units tesla or gauss.
Field lines of magnets
Field lines can be used to visualise a magnetic field. The field lines of magnetic fields always run in closed loops and, therefore, have no beginning and no end. The reason why the field lines form closed loops is exactly because the magnetic field is source-free, i.e. it always has a north pole and a south pole.If you start at the north pole of a magnet, the field lines run vertically away from the surface of the north pole of the magnet and curve towards the south pole until they arrive vertically on the surface of the magnetic south pole. Inside the magnetic material itself, the field lines run back to the starting point at the north pole and thus form a closed loop.
The force effect of the magnet on a magnetic test piece, for example a compass needle, is proportional to the density of the field lines. The compass needle is orientated tangentially to the field lines.
Experimentally, you can get an idea of the existence of the magnetic field around the magnet by scattering iron filings on a sheet of paper with a magnet placed underneath. The iron filings then arrange themselves in curved patterns, which can be understood as an image of the field lines.
The north pole and the south pole of a magnet are determined by definition. The field lines, by definition, run from the north pole to the south pole. This means that there is no physical principle that determines which pole of a magnet is the north pole and which is the south pole.
Difference between magnetic north pole and geographic North Pole
Illustration 1: Globe with geographic and magnetic poles of the Earth.
While the geographic North Pole is defined by the intersection point of Earth's axis (red) in the direction of the North Star, it is the magnetic south pole of the Earth that is located nearby, and to which compass needles are aligned (green dot).
The magnetic north pole (red dot) is located near the southern intersection point of the rotational axis.
Earth also has a magnetic field as an invisible protective shield against cosmic radiation and solar wind.
This is caused by underground currents in the Earth's liquid interior.
However, the North Pole of the Earth is defined as the point of intersection of Earth’s imagined rotational axis and Earth’s surface in the direction of the North Star.
This point is, therefore, referred to more precisely as the 'geographic North Pole'.
Although one of the Earth's magnetic poles is located near the geographic North Pole, this is actually the magnetic south pole of the globe.
The north pole of a compass needle points north because that is where the Earth's magnetic south pole is located, which is close to the geographic North Pole (Illustration 1).
To find out how to build your own compass, take a look at The world's most simple compass.
Earth's magnetic field
Illustration 2: Earth's magnetic field, which directs the solar wind around the Earth or partially captures it at the poles.
(Source: Herbert Bolz, CC BY 4.0,
via Wikimedia Commons)
Created by the movement of liquid iron in the Earth's outer core, the magnetic field
extends far into space and thus protects life on our planet from the high-energy particles of the solar wind (Figure 2).
The poles of the magnetic field, as mentioned – not to be confused with geographical poles, are in constant motion.
This movement of the poles is caused by changes in the circulation of the liquid core material.
It is also worth noting that the Earth's magnetic field occasionally reverses, a phenomenon in which the magnetic north pole becomes the south pole and vice versa.
These pole reversals, which occur over thousands of years, are part of a natural cycle, the exact causes of which are still being researched.
Understanding the Earth's magnetic field is not only important for science; it also plays a crucial role in navigation and many technological applications.
How are Northern Lights created?
Northern Lights, also known as Aurora Borealis, are caused by interactions between charged particles of the solar wind and the Earth's magnetosphere. These particles are directed to the poles by the Earth's magnetic field, where they collide with gas atoms and molecules in the upper atmosphere and cause them to glow. The Earth's magnetic field acts as a guidance system, guiding the particles along the magnetic field lines to the polar regions and allowing the glowing aurorae to form in these areas. This leads to fascinating, moving, often greenish, luminous phenomena, which can be observed in clear weather, especially in northern latitudes.How do migratory birds orient themselves by the Earth's magnetic field?
Migratory birds use the Earth's magnetic field as a navigation aid by being able to perceive the magnetic fields through specialised sensory cells and thereby obtain directional orientation. These sensory cells, often located in the eye or beak area, allow birds to "see" or sense magnetic field lines, which helps them to orient themselves on their long migrations between breeding and wintering grounds. This magnetic sense complements other methods of navigation, such as orientation by stars, the sun and geographical landmarks, and is a fascinating example of the adaptability of wildlife to natural phenomena.
Author:
Dr Franz-Josef Schmitt
Dr Franz-Josef Schmitt is a physicist and academic director of the advanced practicum in physics at Martin Luther University Halle-Wittenberg. He worked at the Technical University from 2011-2019, heading various teaching projects and the chemistry project laboratory. His research focus is time-resolved fluorescence spectroscopy in biologically active macromolecules. He is also the Managing Director of Sensoik Technologies GmbH.
Dr Franz-Josef Schmitt
Dr Franz-Josef Schmitt is a physicist and academic director of the advanced practicum in physics at Martin Luther University Halle-Wittenberg. He worked at the Technical University from 2011-2019, heading various teaching projects and the chemistry project laboratory. His research focus is time-resolved fluorescence spectroscopy in biologically active macromolecules. He is also the Managing Director of Sensoik Technologies GmbH.
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