Principles of Magnetism and Laws

  • Principles of Magnetism and Laws

Principles of Magnetism and Laws


Principles of Magnetism and the Magnetic Field

Magnetism is a natural phenomenon of behavior between two or more matter where attraction or repulsion takes place. A matter that possesses this magnetic property are called magnets.

Magnets have an area of influence - called the Magnetic Field that can affect another magnet. Within this region, magnetic forces are observable.



Nature of Magnetic Materials

There are several components as why materials possess magnetic properties. The simple atomic model where an electron orbits around the nucleus is actually analogous to a small current loop where a miniscule electric current is generated. This causes each atom contribute a magnetic reaction to the material producing a magnetic field. However, the net magnetic field is zero due to the opposing atoms cancelling each other’s magnetic fields. The material does not show magnetic effects unless an external magnetic field is applied.

Electrons in orbit generates electric current which contributes to the magnetism of atoms

Other contributors to the magnetic properties of a material are the electron spin and nuclear spin. In an atom with many electrons present, the electron spin in unfilled shells contributes to the magnetic moment for the atom. Nuclear spin however, has a miniscule effect to the net magnetic property.

If a magnet is broken into pieces, each piece becomes its own separate magnet. Most magnets lose their property when heated enough or dropped from a height. A magnet can also impart its properties to any magnetic material.


Properties of Magnets

There are six classifications of materials according to their magnetic characteristics:

  1. Diamagnetic – This material has an internal net magnetic moment of zero, thus, will produce no magnetic reaction. (eg. Copper, Gold, Silicon, metallic bismuth and other inert gases)
  2. Paramagnetic – This material has atoms where electron spin and orbital motion do not quite cancel and shows no magnetic effects in the absence of an external magnetic field. When an external magnetic field is applied, however, it will produce a small torque and tends to become aligned with the external field. (eg. Potassium, Oxygen, Aluminum and other rare earth metals)
  3. Ferromagnetic – Each atom has a relatively large dipole moment, caused mainly by uncompensated electron spin moments. The forces within the atoms cause such atoms to be aligned with the applied field in parallel fashion. These regions of magnetically aligned atoms are called domains. (eg. Iron, Nickel, Cobalt at below Curie temperature (1043 K))
  4. Antiferromagnetic – the forces between the adjacent atoms cause atomic moments to line up in antiparallel fashion. Their net magnetic moment is zero and are only affected slightly by the presence of an external magnetic field. This is only present to materials at relatively low temperatures, and not of importance when it comes to engineering.
  5. Ferrimagnetic – also shows antiparallel alignment as antiferromagnetic materials, however, their atomic moments are not equal. Shows large response to an external magnetic field, although not as large as that in ferromagnetic. It also has greater resistance than ferromagnetic and also disappears above Curie temperature.
  6. Superparamagnetic – Composed of assemblage of ferromagnetic particles in a nonferromagnetic lattice.


Field Pattern of Bar Magnets

All magnets have two poles, conventionally called “north” and “south”. These poles are the pointing direction of the alignment of atoms and the direction of the magnetic field. The point in which the arrow escapes the body is the North Pole and the end point is the South Pole.

These imaginary lines of force are called the magnetic flux and radiates from the conventional North Pole to the South Pole and then back to the North Pole through the material.

North and South Magnetic Poles
North and South Magnetic Poles



Properties of Magnetic Flux

Magnetic flux (symbol: Φ) are imaginary lines that represent the magnetic field. It has the following characteristics:

  • The direction of the line of force radiates from the conventional unit North and then back to the conventional unit South. From then on, it will travel through the object from south to north through the easiest magnetic path.
  • The lines arrange itself so as to establish the maximum number of lines and so that no lines will cross over.
  • The strength of the magnetic field is indicated by how close the lines are.
  • The lines behave like stretched rubber bands and tend to contract lengthwise but expand laterally
  • Magnetic flux tend to spread in free space. This "spreading" is called the fringing effect


Laws on Magnetism

  1. Like poles repel and unlike poles attract
  2. A magnetic field always tends to arrange itself so that the greatest number of lines of force are created.