The generation of electric power depends on magnetism or the principles of magnets. Most of us have seen a magnets' ability to attract certain metals, such as iron. Any material that can attract metals is called a "magnet". The attractive ability of these materials is called "magnetic force". Certain specimens of iron ore possess this attracting property when they are taken from the earth. One name for this material is magnetite or lodestones.
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Magnets
The basic atomic structure of a magnet seems to align most of the molecules in the same direction. It's possible to see this force through a simple experiment:
Put a bar magnet under a sheet of glass and sprinkle iron filings on the glass. The lines of force from the magnet show up clearly as the filings form a pattern. Notice that the attractive forces are greatest at the two ends of the magnet, where the majority of filings gather. We call these ends "poles".
The density of the pattern represents the strength of the field, which is the magnitude of the force exerted upon a magnetic material placed at the point in the field. These lines are called lines of magnetic flux.
If we suspend a magnet by a string from its center so that it is free to turn, it will turn until there axis lines up with its poles, lying along the earth's magnetic north and south poles. The pole which points north is called the north pole and the other is called the south pole. These are usually designated by an N and S marked on the magnets.
Let's add another magnet to our experiment and we will notice another key property of magnets.
The like poles will repel one another, while the unlike poles will attract one another. This is a very important principle since the generation of electric power depends on these laws of attraction.
Almost all commercially available magnets are artificial. They were manufactured to be magnets by using other magnets to create the correct molecular alignment.
There are two types of magnets: temporary and permanent. Temporary magnets are those which will hold their magnetism only as long as the magnetizing force is maintained. These are usually found inside motors.
Permanent magnets are those which will hold their magnetism after the magnetizing force has been removed and will continue to be magnets for as long as they are not disturbed by being jarred or heated.
Electromagnetic Fields
The flow of electricity through a conductor produces both an electric and magnetic field around the conductor. Collectively, these two fields are referred to as an electromagnetic field or EMF. The strength of the electric field is measured in volts per meter and varies with the amount of the source voltage. The higher the source voltage, the higher the strength of the field. Electric field strength decreases rapidly with distance from the source.
Electric fields are produced both naturally and by any conductor carrying electricity. The strength of the earth's natural electric field varies, but on average is about one-thousandth of a volt per meter. Electric field strength typically varies from 10 to 150 volts per meter under electric distribution lines and 5 to 100 volts per meter inside homes and workplaces.
The strength of a magnetic field is typically measured in units of gauss or milligauss and varies with the amount of current moving through a conductor. Lines or devices requiring high levels of current flow produce stronger magnetic fields than those with low current flow. For example, the measure of a magnetic field directly under a high voltage transmission line is somewhere between 20 to 650 milligauss. The magnetic field measured underneath a lower power distribution line is .5 to 30 milligauss.
Magnetic fields produced by electrical circuits drop off rapidly with distance from the source. The magnetic field produced by a microwave at 1 foot is 70 to 100 milligauss while at five feet away, the magnetic field strength drops to five milligauss.
Electric fields are blocked by shielding such as walls, houses, trees, other vegetation, soil, and other large dense objects. Magnetic fields, on the other hand, pass easily through most objects and are only blocked by structures containing large amounts of iron or iron alloy metals.
Electromagnets
Electromagnets play an essential role in the operation of generators, motors, transformers, and relays. Electromagnets are constructed by wrapping an insulated conductor wire around an iron object, like a large nail, and then passing an electrical current through the wire. The strength of the electromagnet depends on the number of wraps, the size of the wire, and the amount of current flowing through the wire.
Michael Faraday discovered in 1831 that if a coil of copper wire is rotated in a magnetic field in such a way as to cut across the lines of magnetic force, an electric charge is created or induced in the wires. This is the basic principle by which practically all our present day electric current is generated.
Generators use magnetic induction to produce electrical energy. Electrical current is generated by moving wires through a magnetic field. The wire loop inside the generator is mechanically driven by some source of rotary motion. The source of power for the rotation might be fossil fuels, falling water or nuclear energy. As the wire loop spins inside the magnetic field, an electric current is produced in the wire. This current becomes the basis for commercially available electrical energy.
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