Magnetism
In this blog post I would like to explain the overall basics of how Magnetism and Magnetic Materials work, as I currently understand it to be.
Magnetic Materials
To best understand the principles of electricity, it is necessary to study magnetism and the effects of magnetism on electrical equipment. Magnetism and electricity are both so closely related to one another that the study of either subject would be incomplete without at least a basic knowledge of the other.
Most, if not all, of today's modern electrical and electronic equipment could not function without magnetism. If it requires electricity to function, then it uses and relies on magnetism to some degree.
Magnetism is generally defined as that property of a material which enables it to attract pieces of iron. A material possessing this property is known as a Magnet. Materials that are attracted by a magnet, such as iron, steel, nickel, and cobalt, have the ability to become magnetized, and these type of materials are called Magnetic Materials.
Non-Magnetic Materials
Other types of materials, such as paper, wood, glass, or tin, which are not attracted by magnets, are considered Nonmagnetic. Nonmagnetic materials are not able to become magnetized (under normal room temperature conditions and environments).
Ferromagnetic Materials
Ferromagnetic materials are those which are relatively easy to magnetize, such as iron, steel, cobalt, and the alloys Alnico and Permalloy. Ferromagnetic materials are the most important group of materials connected with electricity and electronics today.
An alloy is made from combining two or more elements, one of which must be a metal. These new alloys (Alnico and Permalloy) can be very strongly magnetized, and they are capable of obtaining a magnetic strength great enough to lift Five Hundred Times their own weight.
Natural magnets are magnetic stones that are magnetized by a natural process, without any intervention or influence from humans. These stones have the ability to attract small pieces of iron in a manner similar to the magnets which are commonly used today. Natural magnets no longer have any practical use, since it is now possible to easily produce much more powerful magnets.
Magnets that are produced from magnetic materials are called Artificial Magnets. They can be made in a variety of shapes, sizes and strengths, and they are used extensively in modern electronics today.
Artificial magnets are generally made from special iron or steel alloys which are usually magnetized electrically, by inserting the material into a coil of insulated wire and then passing a heavy flow of electrons through the wire. Magnets can also be produced by physically stroking a magnetic material with magnetite (a naturally formed magnetic material) or with another artificial magnet. The forces causing magnetization are represented by magnetic lines of force, very similar in nature to electrostatic lines of force.
Artificial magnets are usually classified as being either Permanent or Temporary, depending on their ability to retain their magnetic properties after the magnetizing force has been removed. Magnets made from substances, such as hardened steel and certain alloys, which retain a great deal of their magnetism are called Permanent Magnets. These materials are relatively more difficult to magnetize however, because of the opposition (resistance) offered to the magnetic lines of force as the lines of force try to distribute themselves throughout the material. The opposition that a material offers to the magnetic lines of force is called Reluctance. All permanent magnets are produced from materials that have a high reluctance. Once the high reluctance material becomes magnetized, they resist changing back (hence, they are reluctant to change), and therefore they retain their magnetic state until some external influence forces them to again change.
The difference between a permanent and a temporary magnet has been indicated in terms of reluctance, a permanent magnet has a high reluctance and a temporary magnet has a low reluctance. Materials with low reluctance, such as soft iron or annealed silicone steel, are relatively easy to magnetize, but they will only retain a small part of its magnetism once the magnetizing force is removed. Materials of this type that easily lose most of their magnetic strength are called Temporary Magnets. The amount of magnetism that remains in a temporary magnet is known as its Residual Magnetism. The ability of a material to retain an amount of residual magnetism is called the Retentivity of the material.
Magnets are also described in terms of the Permeability of their materials, or the ease with which magnetic lines of force distribute themselves throughout the material. A permanent magnet, which is produced from a material with a high reluctance, has a low permeability. A temporary magnet, produced from a material with a low reluctance, would have a high permeability.
Magnetic Poles
The two ends of a magnet, which are the regions of concentrated lines of force, are called the Poles of the magnet. Magnets have two magnetic poles (North and South, or N and S) and both poles of a magnet have equal magnetic strength to each other.
The magnetic force surrounding a magnet is not uniform. There exists a great concentration of force at each end of the magnet and a very weak force at the center. Proof of this fact can be obtained by dipping a magnet into iron fillings, and visually seeing the iron fillings collect on the ends of the magnet and not at the magnets center. It can be seen that many filings will cling to the ends of the magnet while very few adhere to the center.
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| Bar Magnet |
Laws of Magnetic Poles
If a bar magnet is suspended freely on a string, it will spin and align itself in a north and south direction. When this experiment is repeated, it is found that the same pole of the magnet will always swing toward the northern geographical poles direction of the earth. Therefore, that pole of the magnet is called the north-seeking pole, or simply the North Pole. The other pole of the magnet is the south-seeking pole, or the South Pole.
A practical use of the directional characteristic of the magnet is the compass, a device in which a freely rotating magnetized needle indicator points toward the geographical planetary North Pole (or the North Pole of Earth if used here on Earth, or the North Pole of some other planet if used on that other planet - assuming that other planet has an iron core). The realization that the poles of a suspended magnet always move to a definite position gives an indication that the opposite poles of a magnet have opposite magnetic polarity.
The law previously stated regarding the attraction and repulsion of charged bodies may also be applied to magnetism if the pole is considered as a charge. The north pole of a magnet will always be attracted to the south pole of another magnet and will show a repulsion to another north pole, just as the south pole of a magnet will always be attracted to the north pole of another magnet and will show a repulsion to another south pole..
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| Reaction Between Magnetic Poles |
The law for magnetic poles is: Like poles repel, unlike poles attract.
Comic Relief
I must humbly admit that I can claim that I too am like a magnet when it comes to Women, because magnets repel as well, LOL (I thought it was funny).
The Earth's Magnetic Poles
The fact that a compass needle always aligns itself in a particular direction, regardless of its position or location on Earth, indicates that the Earth is a huge natural magnet. The distribution of the magnetic force about the Earth is the same as that which might be produced by a giant bar magnet running through the center of the Earth.
The Earth actually has two North Poles. It has a Geographical North Pole, as defined by stable latitude and longitude map coordinates, and a Magnetic North Pole, as defined by an unstable convergence location of Earths natural magnetic line of forces. The same is true for Earth's South Poles as well. The ability of the north pole of the compass needle to point toward the general location of the north geographical pole of Earth is simply due to the presence of Earths magnetic north pole being nearby. At the time of this writing, the two North Poles of Earth are approximately 500 kilometers (about 310 miles) away from each other, and appears to slowly be moving further apart from each other every year in an accelerated increasing rate (i.e. the Polar Shift).
Conflict Of Terminology
The Earths northern magnetic pole is named the magnetic North Pole, however, in actuality, it must have the polarity of a south magnetic pole since it attracts the north pole of a magnetized compass needle. The reason for this conflict in terminology can be traced back in history to the early users of the compass several hundred years ago. Since those early users of the compass knew very little about magnetic effects, they called the end of the compass needle that they believed pointed towards the north geographical pole, the north pole of a compass. With our present knowledge of magnetism, we now know that the north pole of a compass needle can be attracted only by an unlike magnetic pole, that is, a pole of south magnetic polarity.
It has not yet been corrected in schools and global society mainly (but not entirely) because it is unclear which labeling is correct and which is incorrect: is it the names of the poles of a magnet that are incorrectly labeled or is it the names of the poles of earth that are incorrectly labeled? Another reason why nobody corrects this yet is to simply maintain a global industry standard for reference purposes.
Magnetic Fields
The space surrounding a magnet where magnetic forces act is known as the magnetic field.
Experiments have shown that the magnetic field is very strong at the poles and weakens as the distance from the poles increases. It is also apparent that the magnetic field extends from one pole to the other, constituting a loop about the magnet.
By definition, the Magnetic Lines Of Force are imaginary lines used to simply visually illustrate and describe the pattern of the magnetic field. The magnetic lines of force are assumed to emanate from the North Pole of a magnet, pass through the surrounding space around the outside of the magnet, and enter back into the South Pole of the magnet. The lines of force then travel inside the magnet from the South Pole to the North Pole, thus completing a closed loop.
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| Bar Magnet Lines Of Force |
Although magnetic lines of force are imaginary, a simplified version of many magnetic phenomena can be explained by assuming that the magnetic lines have certain real properties. The lines of force can be compared to rubber bands which stretch outward when a force is exerted upon them and contracted when the force is removed.
When two magnetic poles are brought close together, the mutual attraction or repulsion of the poles produces a more complicated pattern than that of a single magnet. These magnetic lines of force can be plotted by placing a compass at various points throughout the magnetic field, or they can be roughly illustrated by the use of iron filings and allowing the iron filings to align themselves with the magnets magnetic lines of force.
The characteristics of magnetic lines of force can be described as follows:
- Magnetic lines of force are continuous and will always form closed loops.
- Magnetic lines of force will never cross one another.
- Parallel magnetic lines of force traveling in the same direction repel one another. Parallel magnetic lines of force traveling in opposite directions tend to unite with each other and form into single lines traveling in a direction determined by the magnetic poles creating the lines of force.
- Magnetic lines of force tend to shorten themselves. Therefore, the magnetic lines of force existing between two unlike poles cause the poles to be pulled together.
- Magnetic lines of force pass through all materials, both magnetic and nonmagnetic.
- Magnetic lines of force always enter or leave a magnetic material at right angles to the surface.
Magnetic Effects
| Magnetic Flux | : | The total number of magnetic lines of force leaving or entering the pole of a magnet is called Magnetic Flux. The number of flux lines per unit area is known as Flux Density. |
| Field Intensity | : | The intensity of a magnetic field is directly related to the magnetic force exerted by the field. |
| Attraction / Repulsion | : | The intensity of attraction or repulsion between magnetic poles is directly proportional to the product of the pole strengths, and inversely proportional to the square of the distance between the poles. |
Theories Of Magnetism
Two main theories of magnetism being taught today are the Weber's Theory and the Domain Theory.
The Weber's Theory considers the molecular alignment of the material. This theory assumes that all magnetic substances are composed of tiny molecular magnets. Any unmagnetized material has the magnetic forces of its molecular magnets neutralized by adjacent molecular magnets, thereby eliminating any magnetic effects. A magnetized material will have most of its molecular magnets lined up so that the north pole of each molecule points in one direction, and the south pole faces the opposite direction. A material with its molecules thus aligned will then have one effective north pole, and one effective south pole.
The more modern Domain Theory is based on the electron spin principle. From the study of atomic structure of Matter, it is known that all matter is composed of vast quantities of atoms, where each atom contains one or more orbital electrons. The electrons are considered to orbit in various shells and sub-shells depending upon their distance from the nucleus (i.e. center) of that atom. The structure of the atom has previously been compared to the solar system, wherein the electrons orbiting the nucleus correspond to the planets orbiting the sun (although I believe it is more accurate to visualize its shells as being more 3D spherical than 2D flat). It has been experimentally proven that an electron has a magnetic field about it along with an electric field. The effectiveness of the magnetic field of an atom is determined by the number of electrons spinning in each direction. If an atom has equal numbers of electrons spinning in opposite directions, the magnetic fields surrounding the electrons cancel one another, and the atom is unmagnetized. However, if more electrons spin in one direction than another, the atom is magnetized.
Magnetic Induction
All substances that are attracted by a magnet are capable of becoming magnetized. The fact that a material is attracted by a magnet indicates the material must itself at least be temporarily a magnet at the time of attraction (in order to have unlike magnetic poles that attract).
As an iron needle is brought close to a bar magnet, some flux lines emanating from the north pole of the magnet pass through the iron needle in completing their magnetic path. Since magnetic lines of force travel inside a magnet from the south pole to the north pole, the needle will be magnetized in such a polarity that its south pole will be adjacent to the north pole of the bar magnet. As a result of this, there now exists an attraction between the two magnets.
If another iron needle is placed in contact with the end of the first iron needle, it would be magnetized by induction. This process could be repeated until the strength of the magnetic flux weakens as distance from the bar magnet increases. However, as soon as the first iron needle is pulled away from the bar magnet, all the needles will fall. The reason being that each needle becomes a temporary magnet due to low reluctance, and as soon as the magnetizing force is removed, their domains (electron spin directions) once again assume a random distribution.
Magnetic induction will always produce a pole polarity on the material being magnetized opposite that of the adjacent pole of the magnetizing force. It is sometimes possible to bring a weak north pole of a magnet near a strong magnet north pole and observe attraction between the poles. The weak magnet, when placed within the magnetic field of the strong magnet, has its magnetic polarity reversed by the field of the stronger magnet. Therefore, it is attracted to the opposite pole. For this reason, you should try and always keep the very weak magnets, such as a compass needle, away from very strong magnets.
Magnetism can be induced in a magnetic material by several means. The magnetic material may be placed in the magnetic field, brought into contact with a magnet, or stroked by a magnet. Although stroking and contact both indicate actual physical contact with the material, they are still considered in magnetic studies as magnetizing by Induction.
Magnetic Shielding
There is no known insulator for magnetic flux. If a nonmagnetic material is placed in a magnetic field, there is no appreciable change in flux, and the flux effortlessly penetrates the nonmagnetic material.
If a magnetic material is placed in a magnetic field, the flux may be redirected to take advantage of the greater permeability of the magnetic material. Permeability is the quality of a substance which determines the ease with which it can be magnetized.
The sensitive mechanisms of electric instruments, circuits, and meters can be influenced by stray magnetic fields which will cause errors in their readings and functions. Because instrument mechanisms cannot be insulated against magnetic flux, then it is necessary to employ some means of re-directing the unwanted magnetic flux to travel around the instrument. This is accomplished by placing a soft-iron case, called a Magnetic Screen or Shield, about or around the instrument. Taking the path of least resistance, the flux is established more readily through the iron (even though the physical path is longer) than through the air inside the case, resulting in the instrument to be effectively shielded from the unwanted magnetic flux.
Magnet Shapes
Because of the many uses of magnets, magnets can be found in various shapes and sizes to best fit their use requirements. However, magnets usually come under one of three general classifications:
- Bar Magnets : commonly used in schools for studying and demonstrating the properties of magnetism.
- Horseshoe Magnets : most frequently used in electrical and electronic equipments. Can produce much stronger magnetic field strengths than bar or ring magnets of the same size, because the magnetic strength from one pole to the other is greatly increased due to the concentration of the magnetic field in a smaller area.
- Ring Magnets (i.e. doughnut magnets) : commonly used in computer memory cores and communication equipment, as well as producing temporary shielding of electrical instruments.
Magnets and Energy
Magnets and magnetic fields can be used in the creation of electrical energy, and electrical energy can be used to make magnets and magnetic fields.
Both AC (alternating current) and DC (direct current) electro-magnetic generators use magnetic fields to produce and generate electricity. These generators produce electricity by either rotating a coil of conductive wire to cut through magnetic fields, or by rotating magnetic fields to sweep across a coil of conductive wire. In either case the end goal is to cause a conductor to cut through the flux of magnetic field lines to induce an electron current flow within the conductive wire.
The armature of the AC or DC generator can be rotated by means of gas engines, turbines (wind, steam, water, etc...), or even by hand cranks on smaller units.
Final Thoughts
Thank you for reading, I hope you found this blog post educational and helpful in some way.