Basic-electrical-theory

LESSON 2 - Basic-electrical-theory

This is a continuation of Module 101 and it is important to understand the basic principles of magnetism

Principles of Magnetism

Understanding the basic principles of magnetism is this is essential to understanding electricity and basic-electrical-theory in general, as well as the many applications found on boats. Magnetism is used to create current flow, and electric current flow causes an associated force

The attraction and repulsion principles of magnetism are used to make electricity perform work. Magnetic principles determine certain reactions; for example, the attraction or repulsion of two magnetically charged objects. These principles can be used in a motor to cause motion and to turn a water pump.

Electricity, in other words, uses the magnetic properties of subatomic particles to develop magnetic fields at a given place and time to perform work. Magnetism and electricity are closely related and the study of either subject would be incomplete without at least a basic knowledge. Electrical motors use magnets to convert electrical energy into mechanical motion. Generators use magnets to convert mechanical motion into electrical energy. Learn about basic-electrical-theory here.

About Magnetic Materials

Magnetism is generally defined as that property of material which enables it to attract pieces of iron. A material possessing this property is a magnet. The word has its origins with the ancient Greeks who found stones with this characteristic. The Greeks called these substances magnetite. The Chinese are said to have been aware of some of the effects of magnetism as early as 2600 B.C. They observed that stones similar to magnetite, when freely suspended, had a tendency to assume a nearly north and south direction. Because of the directional quality of these stones, they are referred to as lodestones or leading stones. Materials that are attracted by a magnet, such as iron, steel, nickel, and cobalt, can become magnetized. These are called magnetic materials. Materials, such as paper, wood, glass, or tin, which are not attracted by magnets, are nonmagnetic. Nonmagnetic materials cannot become magnetized. Learn about basic-electrical-theory here.

The most important materials connected with electricity and electronics are the ferromagnetic materials. Ferromagnetic materials are relatively easy to magnetize. They include iron, steel, cobalt, and the alloys Alnico and Permalloy. An alloy is made by combining two or more elements, one of which must be a metal.

Artificial Magnets

Magnets produced from magnetic materials are called artificial magnets. They can be made in a variety of shapes and sizes and are used extensively in electrical equipment. Artificial magnets are generally made from special iron or steel alloys which are usually magnetized electrically. The material to be magnetized is inserted into a coil of insulated wire. Learn about basic-electrical-theory here.

A heavy flow of electrons is produced by stroking a magnetic material with magnetite 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. Learn about basic-electrical-theory here.

Artificial magnets are usually classified as 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 difficult to magnetize because of the opposition offered to the magnetic lines of force as the lines of force try to distribute themselves throughout the material. The opposition is called reluctance. All permanent magnets are produced from materials having a high reluctance.

A material with a low reluctance, such as soft iron or annealed silicon steel, is relatively easy to magnetize. It retains only a small part of its magnetism once the magnetizing force is removed. Learn about basic-electrical-theory here.

Materials that easily lose most of their magnetic strength are called temporary magnets. The amount of magnetism that remains in a temporary magnet is referred to as its residual magnetism. The ability of a material to retain an amount of residual magnetism is called the retentivity of the material.

The difference between a permanent and temporary magnet is indicated in terms of reluctance. A permanent magnet has a high reluctance, and a temporary magnet has a low reluctance. 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, produced from a material with a high reluctance, has a low permeability. A temporary magnet, produced from a material with a low reluctance, has a high permeability. Learn about basic-electrical-theory here.

Magnetic Poles

The magnetic force surrounding a magnet is not uniform. There is a great concentration of force at each end of the magnet and a very weak force at the center. To verify this dip a magnet into iron filings. You will observe that many filings will cling to the ends of the magnet, while very few will adhere to the center. The two ends, which are the regions of concentrated lines of force, are called the poles of the magnet. Magnets have two magnetic poles, and both poles have equal magnetic strength.

Law of Magnetic Poles

To demonstrate the law of magnetic poles, suspend a bar magnet freely on a string You will observe that it will align itself in a north and south direction. The same pole of the magnet will always swing toward the north geographical pole of the earth. Therefore, it 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 Learn about basic-electrical-theory here.

A practical use of the directional characteristic of the magnet is the compass. The compass has a freely rotating magnetized needle indicator that points toward the North Pole. The poles of a suspended magnet always move to a definite position. This indicates opposite magnetic polarity exists.

The law of electricity 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. The law of magnetic poles is that like poles repel and unlike poles attract. Learn about basic-electrical-theory here.

Magnetic Fields

The space surrounding a magnet where magnetic forces act is the magnetic field. Magnetic forces have a pattern of directional force which can be observed by performing an experiment with iron filings. Place a piece of glass over a bar magnet. Then sprinkle iron filings on the surface of the glass or even use paper. The magnetizing force of the magnet will be felt through the glass, and each iron filing becomes a temporary magnet. Tap the glass gently.

The iron particles will align themselves with the magnetic field or invisible flux lines surrounding the magnet just as the compass needle did previously. The filings form a definite pattern, which is a visible representation of the forces comprising the magnetic field. The arrangements of iron filings indicate that the magnetic field is very strong at the poles and weakens as the distance from the poles increases. They also show that the magnetic field extends from one pole to the other in a closed loop around the magnet. Learn about basic-electrical-theory here.

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 flux lines of force can be plotted by placing a compass at various points throughout the magnetic field, or they can be roughly illustrated using iron filings as before.

The lines of force are similar to an elastic band which will stretch outward when a force is exerted and then contract when the force is removed. Characteristics of magnetic lines of force are 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 extend to unite with each other and form 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 called 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 may be described by a law almost identical to Coulomb's Law of Charged Bodies. The force between two poles is directly proportional to the product of the pole strengths and inversely proportional to the square of the distance between the poles. Learn about basic-electrical-theory here.

Magnetic Induction

All materials than are attracted by a magnet can become magnetized. If a material is attracted by a magnet then this indicates the material must itself be a magnet at the time of attraction. Knowing about magnetic fields and magnetic lines of force simplifies the understanding of how a material becomes magnetized when brought near a magnet.

If an iron nail is brought in close proximity to a bar magnet, some flux lines emanating from the north pole of the magnet will pass through the iron nail in completing their magnetic path. As magnetic lines of force travel inside a magnet from the south pole to the north pole, the nail will be magnetized so its south pole will be adjacent to the north pole of the bar magnet.

Electromagnetism

When a current flows through a conductor (wire or cable) a magnetic field will exist around the conductor. There is a clear relationship between the direction of current flow and the direction of the magnetic field

The Left Hand Rule for conductors is used to demonstrate this relationship. If you grasp or hold a conductor carrying current in the left hand, and point your thumb in the direction of the current flow, the fingers which are surrounding the conductor point in the direction of the magnetic lines of flux

When looking at practical electromagnetism, a coil of wire carrying current forms a magnet. Each loop will generate a small magnetic field. When several coils are added then the field is increased. The left hand rule also applies to coils. If a coil is held, the thumb is pointed towards the North pole of the coil, the fingers point in the flux direction. Learn about basic-electrical-theory here.

In many applications (such as transformers, solenoids, relay coils etc) the coils are wound onto a soft iron bobbin or core. This soft iron conducts magnetic lines of flux easily. When current is applied to the coil, the core is magnetized.

Electromagnetic principles are used in motors, circuit breakers, relays, solenoids, contactors, transformers, starter motors, generators and alternators and more. Learn about basic-electrical-theory here.

Learn about basic-electrical-theory here. More you can learn