For children in particular, but also for many adults, they are among the most fascinating things physics has to offer: Magnets. The beauty of it is that the force behind it, the Magnetismmagnetism can also be observed in everyday life in many places. But what is magnetism in the first place, how does it come about from a physical point of view and what can be done with it? We want to get to the bottom of exactly this phenomenon here.
First of all, we have to distinguish some terms from each other and make them a little more concrete: When talking about magnets and magnetism, many people in their everyday life understand it exclusively as so-called ferromagnetism. We encounter this in many places in our everyday lives, for example on the magnetic board available in countless households, a wall board made of metal or sheet metal to which notes and other everyday objects can be attached with small magnets. If you have a metal refrigerator, you can also simply attach the notes to it with the appropriate magnets. Exactly here we have to do with the mentioned ferromagnetism. This is the magnetic properties of ferrum, better known as iron. We can also observe magnetism in other objects of everyday use, for example in a compass.
It follows: In our everyday lives, we associate objects made of iron and steel in particular with magnets or magnetism. In physics, however, it is known that other materials are also magnetic, for example nickel and cobalt.
Furthermore, many people have misconceptions about the magnetizability of various materials. It is commonly assumed that simple steel is permanently magnetizable. However, this is not correct. Steel, at least when it is not refined, is considered a magnetically soft material. It is magnetisable, but loses this property after a short time. Therefore, care must be taken to use so-called magnetically hard materials for permanent magnetisation. Only these retain their magnetism over a long period of time. This is also the reason why compass needles cannot be made of simple steel wire, which is also magnetically soft.
It is very easy to check whether an object is magnetic by using a permanent magnet. If the permanent magnet comes close to the object, a magnetic force can be felt on it, provided the object is magnetic. The object is thus attracted. However, this cannot be used to check whether the object is permanently magnetic. To determine this, the cross-check must be made. A piece of magnetised material, for example iron or steel, is placed close to the object. If this test object is attracted, it is a permanently magnetised object.
In our everyday life, magnetism is partly desired, but also partly undesired. For example, tools are intentionally magnetized to make them easier to handle. The best example of this are screwdrivers whose tips are magnetized so that they hold the screw in question by themselves. Anyone who has ever worked with such a screwdriver will certainly appreciate the magnetic tip.
The history of magnetism
Before we get into the technical intricacies of magnetism, you should first know since when magnetism has been known to man at all, and thus since when it can be used for his purposes. One of the oldest objects that specifically uses magnetism is the compass. However, the principle behind it was already used before people knew about the exact background. Long before the birth of Christ, advanced peoples used so-called magnetic iron stones to determine the respective cardinal direction.
It was finally the Roman poet Lucretius who named these stones after a landscape in Greece and thus gave them the characteristic name Magnesia. This eventually developed into the terms magnet and magnetism, which are still known today.
In the Middle Ages, the properties of magnetism were first used to magnetize special metallic needles and to use them in a compass as we know it today. It was in particular the English naturalist Alexander Neckam who researched in this field and made corresponding records.
However, the fundamental causes of magnetism remained unexplored until well into the 18th century. Knowledge of the lines of force of magnets and other fundamentals of magnetism were only discovered and documented relatively recently. This also applies to the connection between electric current and magnetism, which was discovered by Hans-Christian Orsted in 1820. Today, his work is considered the basis for modern electrical engineering.
Magnetism as a physical phenomenon
In physics, magnetism is a phenomenon that manifests itself as a force between magnetized objects. Magnetism is also manifested in objects with moving electrical charges, for example, conductors with current flowing through them. The environment in which the said force takes place is called the magnetic field. It is therefore the force field generated by a magnetized object. Magnetic fields can have a reciprocal effect, i.e. an object can generate a magnetic field itself and also be influenced by another magnetic field.
In order to document the force effects of the magnetic fields, so-called field lines are used. They show the course of the force in the magnetic field. The distance between the magnetic field lines represents the strength of the field. The closer the field lines are together, the stronger the magnetic field. All magnetic field lines run in the form of closed paths, so there is no beginning and no end to such a field line. To make the field lines visible, we use either a compass needle or alternatively iron filings.
The earth, man and magnetism
Magnetism plays a major role on our earth. Provided that no other force is acting, a magnetic object would always align itself with one of its ends in the direction of the north, while the other end thus points in the direction of the south pole. Exactly for this reason one also speaks of north and south pole. In science, it is assumed that the field lines of a magnet exit at the north pole and re-enter at the south pole.
Since we humans are a significant part of planet Earth, magnetic fields are also constantly acting in our bodies. These result from the activity of our nerves, which consists of electric current. This current in turn produces very weak magnetic fields, which can, however, be documented with sensitive measuring instruments. Thus, in reverse, magnets can have an influence on the human nervous system, as has already been scientifically documented in many experiments. Therefore, especially in medicine, the power of magnetism is used for various purposes, for example to stimulate muscles or nerves.