The Laws of Magnets

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The Laws of Magnets
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The laws of magnetism have had a profound effect on science and culture. Since the early years of the 19th century, scientists have worked to identify and explain the various physical laws governing the behavior of magnets in a variety of contexts. By 1905, the scientific understanding of magnetism evolved to the point that it helped drive the creation of Einstein's theory of special relativity. Although a detailed, in-depth understanding of magnetism requires extensive effort, you can gain a broad overview of these fundamental laws relatively quickly.


Exploring the First Law of Magnetism

The laws of magnetism have been developed and refined extensively since the experiments of Orsted, Ampere and other now-famous scientists in the early 1800s. The most fundamental law introduced during this time is the concept that the poles of a magnet each have their own distinct positive or negative charge and only attract oppositely charged poles. For example, it is nearly impossible to keep two positively charged magnetic poles from repelling each other. On the other hand, it is difficult to keep a positively charged and negatively charged magnetic pole from attempting to move toward each other.


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Where this concept becomes particularly interesting is when a pre-existing magnet is cut into two different, smaller magnets. Following the cut, each of the smaller magnets has its own positive and negatively charged poles, irrespective of where the larger magnet was cut.

The concept of oppositely charged poles is commonly referred to as the First Law of Magnetism.

Defining the Second Law of Magnetism

The second law of magnetism is slightly more complex and relates directly to the electromotive force of the magnets themselves. This particular law is commonly referred to as Coulomb's Law.


Coulomb's law states that the force exerted by the pole of a magnet on an additional pole adheres to a series of strict rules, including:

  • The force is in direct proportion to the product of the forces of the pole.
  • The force exists in inverse proportion to the square of the middle distance between the poles.
  • The force is dependent on the specific medium in which the magnets are placed.

The mathematical formula commonly used to represent these rules is:


F = [K x M1 x M2)/d2]

In the formula, M1 and M2 represent the strengths of the poles, D is equal to the distance between the poles, and K is a mathematical representation of the permeability of the medium in which the magnets are placed.

Additional Considerations About Magnets

The Domain Theory of Magnetism provides additional insight into the behavior of magnets. First introduced in 1906 by Pierre-Ernest Weiss, the theory of magnetic domains seeks to explain the changes that occur inside a substance when it becomes magnetized.


Large magnetized substances consist of smaller areas of magnetism, commonly referred to as domains. Within each domain are smaller units referred to as dipoles. The complex nature of magnetic composition allows for the continued presence of magnetism when larger magnetic units are broken or separated.

Understanding How Demagnetization Occurs

Magnets do not remain magnetized forever. Deliberate demagnetization can occur through the reorganizing of dipoles within the magnet itself. A variety of processes can be used to make this happen. Heating a magnet past its Curie point, which is the temperature at which it is known to manipulate dipoles, is one popular method. Another method for demagnetizing a substance is to apply alternate current to the magnet. Even without applying any of these methods, a magnet slowly demagnetizes over time as part of a natural degradation process.