Magnetic Field

Magnetic fields are produced by electric currents and by magnets at all points in the space around it. It can be either macroscopic currents in wires, or microscopic currents associated with electrons in atomic orbits. The magnetic field B is defined in terms of force on moving charge in the Lorentz force law. The interaction of magnetic field with charge leads to many practical applications. Magnetic field sources are essentially dipolar in nature, having a north and south magnetic pole. The SI unit for magnetic field is the Tesla, which can be seen from the magnetic part of the Lorentz force law Fmagnetic = qvB to be composed of (Newton x second)/(Coulomb x meter). A smaller magnetic field unit is the Gauss (1 Tesla = 10,000 Gauss).

When a conductor is exposed to a magnetic field an electrical current is produced. By constantly reversing its polarity, the electrical current fluctuates back and forth in the opposite direction. This fast and constant reversal of the electrical current direction is called alternating current (AC).

Permanent magnets are objects that produce their own persistent magnetic fields. All permanent magnets have both a north and a south pole. Like poles repel and opposite poles attract. The magnetism in a permanent magnet arises from properties of the atoms, in particular the electrons, that compose it. Each atom acts like a little individual magnet. If these magnets line up, they combine to create a macroscopic magnetic effect. For more details about what happens both microscopically and macroscopically, see the article ferromagnetism.

Alternating Current (AC)

Alternating current is an electric current that repeatedly reverses its flow of electrons back and forth 60 times per second, or 60 Hertz, as opposed to direct current, whose direction remains constantly in one way. So, in other words, alternating current, or AC, means that the electrical current is alternating directions in a repetitive pattern. The usual waveform of an alternating current (AC) power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.

Used generically, AC refers to the form in which electricity is delivered to businesses and residences. The electrical current in your house is alternating current. This comes from power plants that are operated by the electric company. Those big wires you see stretching across the countryside are carrying AC current from the power plants to the loads, which are in our homes and businesses.

Alternating current is generated when a conductor is exposed to a magnetic field that constantly changes its polarity. At a power plant, an electrical generator rotor rotate a coil of wire connected to magnets to create an artificial magnetic field that constantly reverses polarity, inducing an alternating current on the generator stator coils of wire. This rotating magnetic field was invented by Nicolas Tesla, an American inventor born in Croatia.