What is a magnetic field? How can we calculate its strength?

We know that a magnetic field consists of a north pole and a south pole, and these create a magnetic field with a concrete force.

What is a magnetic field?

Each permanent magnet and, of course, each electromagnet is surrounded by a magnetic field around it. The stronger the magnetic field, the closer it is to the permanent magnet, the faster it decreases as the distance with it increases. To illustrate a magnetic field, one uses its magnetic field lines, which surround the magnetic body. The magnetic field lines are autonomous, curved lines that extend outside the body of the magnet always from the north pole to the south pole and inside the body of the magnet towards the north pole. The magnetic field lines always emerge perpendicularly from the body of the magnet.


Magnetic field lines and calculating the strength of their magnetic field

The permanent magnet has no magnetic properties prior to magnetization. This is due to the fact that its elemental magnets are not yet rectified. This required rectification is done by applying an external magnetic field to the permanent magnet. The effects of the magnetic field lines can only be measured outwards if a sufficient number of elementary magnets are rectified. The magnetic field strength is physically indicated by the letter H and has the unit in amperes per metre. For an accurate detection of the magnetic properties, another quantity is required, the magnetic flux density (B), which is provided in units of Tesla (T) or Gauss (G) (1 T = 10 4 G).

The magnetic flux density and magnetic field strength are as follows:

H = B / μ 0 / μ r


μ 0 = magnetic field constant = 1.256 * 10 -6 Vs / A / m

μ r = relative permeability constant


For vacuum and for air, μ we establish r that is approximately equal to 1. For iron and other ferromagnetic materials, μ r can assume remarkable values of a few thousand. If the dependence of magnetic flux density B on magnetic field strength H in a coordinate system with H as abscissa and B as ordinate is plotted, the curve starts at one that is not yet magnetized.

This curve is also called a new curve. By applying an external magnetic field to the permanent magnet to be magnetized, its elementary magnets begin to align in a particular direction and uniformly. The new curve reaches its maximum value B S when all the elementary magnets are aligned. This B S value is the saturation point.


If now the strength of the external magnetic field is reduced again, a certain delay of the decrease of the magnetic flux density is shown. The magnetization curve no longer follows the path of the new curve, but takes a different path due to this delay. This results in a magnetic field strength of 0, the magnetic flux density of the permanent magnet still has a certain positive value B R, the remanence value. To return this remanence value 0, the force of the magnetic field in the negative direction must be further reduced by the negative coercive force -HC.

If the magnetic field strength is further reduced in the negative direction, the negative saturation point -BS is finally reached. At this negative saturation point, all elementary magnets are oriented in the opposite direction to B s. The increase of the magnetic field strength to B S results in a mirror image magnetization curve. This phenomenon is called hysteresis and can be found in all permanent magnets, although to different degrees, depending on the magnetic material used.


Ferrite magnets and other types of magnets, factors that can affect your magnetic fields

Ferrite magnets are among the permanent ceramic magnets with high temperature resistance up to 250°C. The magnetic field strength and magnetic flux density are influenced by very specific factors. When a current-carrying conductor vertically penetrates a plane, a magnetic field forms around the conductor in the form of a right-hand screw. Depending on the current and resistance of the conductor, this magnetic field has a higher or lower magnetic field strength H. If the space around the conductor is completely filled with iron or other ferromagnetic material instead of air, this leads to a strong magnetic field strength. Increased magnetic flux density B. The magnetic flux density is more or less pronounced depending on the ferromagnetic material used around the conductor.

0 and the relative permeability constant r. μ 0 enters the physical relationship H = B / μ 0 / μ r as a fixed amount of 1,256 * 10 -6 Vs / A / m, while μ r as the relative permeability constant can assume very different values depending on the ferromagnetic material used.



A distinction is made between soft and hard magnetic materials. Soft is the term used when the coercive force is relatively small and the hysteresis curve is weak. Magnetically hard substances, on the other hand, have a high coercive field strength and, therefore, a pronounced hysteresis. Whatever your magnetic problems, take advantage of the help we can offer you. Talk to us at any time.

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