• Aluminum-nickel-cobalt
• Barkhausen effect

Attraction and repulsion of a magnet

When a magnet approaches a ferromagnetic material, an attractive magnetic force acts between the two bodies. This is so strong even with small magnets that you can clearly feel them. The cause of a magnetic force are small electrical currents or moving charges: Tiny circular currents at the atomic level are responsible in a permanent magnet for it to exert a magnetic force. Electromagnets in turn only work through a coil through which a current or a moving charge flows. In electrostatics there are electrical forces, which in turn emanate from static charges and at the same time act on other charges. In addition, there is an electric field in electrostatics even if only one pole is present.

A magnetic force describes the force that exists between two moving charges.
The basis of all force effects in physics are the three basic forces: nuclear power, gravity and electromagnetism.

The nuclear forces play a role in the atoms themselves and are the reason why they literally do not "diverge" - in normal everyday life you do not actually get anything with them. There may be one exception: with the energy source of nuclear fusion just beginning to develop, the importance of nuclear forces and the idea of ​​it could reach a much larger number of people directly.

Anyone can imagine something below: The gravitational forces play a role in very large masses - for example, the moon is forced by the gravitational force between the earth and the moon on a circular orbit around the earth. If the gravitational force were not there, the moon would fly tangentially to its orbit, as would the humans and all other bodies on the spinning Earth.

Since the nuclear forces are beyond our direct perception and gravitation only plays a role when it comes to the weights of bodies on Earth, any other forces that can otherwise be measured in any way are electromagnetic in nature - for example, the attraction between a positive and negative charge or between the north and south poles of two magnets. A positive electric point charge and a negative electric point charge attract each other. Just as well would be repelled the same electric charges. Accordingly, there is a so-called electric field between the two charges, which can be imaged with field lines. However, this electric field also starts from a single charge. But when it comes to magnets, magnetic charges can not be used. In addition, a South Pole or North Pole never exists alone. Instead, magnetic forces are triggered by tiny circular currents and the resulting magnetic moments at the atomic level.
The electron spin of the free electron of each atom is usually the strongest elementary magnet of the material. If a large part of the magnetic moments or the elementary magnets are aligned in parallel, magnetization is mentioned. Then the material has a north and a south pole - the two poles always coexist, due to the orientation of the individual spins. The magnetic forces in turn always act along the magnetic field between the north and south poles. It can also be illustrated by field lines. With the density of these field lines, the magnetic force increases. Furthermore, the field lines outside the magnet always point from the north to the south pole.

In order to align the individual elementary magnets in a controlled manner, a magnetic field is required. If one introduces a ferromagnetic body into such a magnetic field, then the magnetic moments align with it. The orientation of the individual elementary magnets is fixed by the exchange interaction - but only in ferromagnetic materials. If the external magnetic field is removed again after the elementary magnets have been aligned, the exchange interaction ensures that the orientation remains constant. At this point, it is only logical that the orientation can be destroyed again: For this, the energy of the exchange interaction must be overcome. This can be done by supplying thermal, magnetic or mechanical energy. A strong impact, strong external magnetic field or high temperature of the material can cause demagnetization.

Lorentz force
The Lorentz force refers to the force acting on a moving charge in a magnetic field. The Lorentz force is perpendicular to the magnetic field and to the direction of motion of the charge, as long as they are not parallel to each other.

The reason electrical and magnetic forces are combined under electromagnetism are the charges and the forces that they cause in different states of motion: charges in a moving state cause magnetic forces and charges at rest cause electrical forces. Electrodynamics describes this transition between both forces through a transition between both states of motion. The magnetic forces can also be understood on the basis of the principle of the lowest possible energy state: For example, a body falls to the ground because the potential energy is lowest there. Likewise, the energy can be minimized in a system consisting of two magnets, which face each other at a distance: Thus, magnetic energy is located between the two magnets, which is described in each case by the energy product. The field energy in the air is getting smaller with an approach of both magnets. Once the two magnets touch, the air space and thus the magnetic force in it are minimal. At the approach of the magnets, the change in this magnetic energy is therefore proportional to the force, which can be expressed by the following formula with the force F and the energy potential U (0):

Is the change vector of the spatial directions. If the energy change of the energy potential is particularly strong in one direction, a particularly strong force also acts in this direction. The Maxwell equations describe the dependence between currents and charges and electric and magnetic fields. However, they are very expensive to solve. An approximation formula would be, for example, the calculation of a magnetic force based on the surface of a solenoid in cylindrical form. The magnetic field H is first calculated using the following approximation. R is the radius and l (small L) the length of the coil. The letter I (large i) indicates the current that flows through the coil: (1)

From a magnetic field H, the magnetic flux density B with the magnetic permeability μ of the material and the magnetic permeability of the vacuum can be determined as follows:(2)

The force F of a cylindrical magnet is calculated according to the following formula, with the pole face A: (3)

Further, the pole face of the cylinder is: (4)

If you put (2) in (3), you get the following: (5)

Using (4) we get: (6)

Now we put (1) in (6) and get our formula for our cylindrical coil with length l and radius R: (7)

For a 5 cm coil with 1000 turns and a radius of 4 cm, which is traversed by a current of 15 A, this would result in a force of about 159.7 Newton. Translated to a realistic example, this would mean that such a coil or such an electromagnet can lift about 16 kg. For such a coil and especially for the big current that's not very much. To amplify the magnetic field or the magnetic energy, an iron core can be used in this course. As a result of the higher magnetic permeability μ, the magnetic force increases by exactly μ multiples.