How can we identify the magnetic force of magnets or magnetic separators?

-          There are different ways of obtaining the magnetic force of magnets or magnetic separators. In the following article we include different formulas to obtain the force.

Magnets, as we all know in everyday life, have both attraction and repulsive forces

What's a magnetic force?

A magnetic force occurs as a consequence of an electromagnetic force, one of the four basic forces of nature, and is caused by the movement of charges. There is a magnetic attraction between two objects containing charge with the same direction of motion. Similarly, charged objects moving in opposite directions have a repulsive force between them.

In our article on magnetic fields, we learned how a moving charge surrounds a magnetic field. The magnetic force in this context is a force generated by the interaction of magnetic fields.

fuerza magnética

How can you calculate the magnetic force of a magnet?

Let's consider two objects. The magnitude of the magnetic force between them depends on how much load moves on each of the two objects and how far apart they are. The direction of the force depends on the relative directions of motion of the load.

The usual way to determine the magnetic force is set in the form of a fixed amount of charge q that moves at a constant velocity v in a uniform magnetic field B. If we do not know the size of the magnetic field directly, we can still use this method because it is often possible to calculate the magnetic field by the distance to a known current. The magnetic force is described in Lorentz's force law as:

                                                                     F = q * v × B

In this way, it is calculated using the cross vector product. We can also calculate the magnitude of the magnetic force by expanding the cross product. The formula related to the angle Phi (less than 180 °) between the velocity vector and the magnetic field vector is:


                                                               F = q * v * B * sinθ


The direction of force can be determined using the Fleming's Right-hand Rule. This rule describes the direction of force as the direction of a "blow" from an open hand. In the right hand rule, the fingers point in the direction of the magnetic field. The thumb points in the direction in which the positive charge moves. If the charge in motion is negative (e.g. Electrons), you must reverse the direction of your thumb because the force acts in the opposite direction. Alternatively, you can use your left hand to align with the negative charge.

Sometimes we want to find the force in a cable through which a current I flows in a magnetic field. This can be done by changing our previous formula. If we remember that speed is a distance / time, we can determine if a cable has a length L.

                                                                      qv = q * L / t

Since the current is the amount of charge flowing per second, the following applies:

                                                                         qv = I * L

and therefore:

                                                                F = B * I * L * sinθ


What factors impact magnetic strength?

The distance between two bodies essentially influences the magnetic force when there is no direct contact between the magnetic separators. The force decreases relatively quickly with increasing distance. A distance of half a millimetre can reduce the force by half. Impurities have a significant impact, as a thin layer of paint on the surface of the magnetic separator reduces the force. Another influence on the magnetic force is the material.

Neodymium magnets, for example, have a higher magnetic force than magnets made of other materials. In addition, the surface condition of the magnetic separator plays an important role in the magnetic force. The more smooth the surface of the magnetic separators, the greater the magnetic force. On the contrary, the rougher the magnetic force, the rougher the surface. Another factor that affects the magnetic force is the thickness of the magnet. If the magnet is too thin, a so-called magnetic saturation is generated.

This saturation causes part of the magnetic field to become useless. Additional factors affecting the magnetic force are environmental conditions such as; temperature, pressure and humidity.

For more information or questions, contact the specialists at ImagnetShop.

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