Electromagnetic Induction

As our industry continues to evolve, electricity appears to be playing an ever more significant role in the operation of aircraft systems.

The aviation industry has always been one that carried a certain mystique. After all it does breach many unknowns. Even after all these years we still refer to our most basic principle as "The Theory of Flight" and not "The Fact of Flight." Attacks from gremlins often stifle our most brilliant minds, and phenomenon such as Saint Elmo's fire is observed on a regular basis. I have even had comments from those many years my senior stating that aviation today is all smoke and mirrors. I know for a fact that this premise does carry some merit as anytime you see the smoke escape from one of these new fangled black boxes, the magic is over.

As our industry continues to evolve, electricity appears to be playing an ever more significant role in the operation of aircraft systems. It was not all that many years ago when mechanical devices and linkages were considered the standards to command the response from engines or even position flight controls. Today's aircraft use computers to regulate engine thrust as well as provide signals to position flight altering servoes. Does the use of this technology stimulate confidence? Consider the definition of electricity courtesy of the Houghton Mifflin Dictionary:The physical phenomena arising from the behavior of electrons and protons that is caused by the attraction of particles with opposite charges and the repulsion of particles with the same charge.

If that doesn't instill confidence, I don't know what would.

Magnetism is another topic associated with wizards and other mystical subjects and again the folks at Houghton Mifflin should be credited for their interpretation: the class of phenomena exhibited by a magnetic field.

What It Is

Electromagnetic induction is the production of an Electro Motive Force (EMF) in a conductor as a result of a changing magnetic field around the conductor. The concept was identified in 1831 by Michael Faraday and independently by Joseph Henry.

Variation in the field around an electrical conductor may be produced by relative motion between the conductor and the source of a magnetic field. This is the principle of an electric generator, by varying the strength of the field around the conductor a constant voltage can be maintained which compensates for variations in electrical load or even variations in the relative motion between the conductor and field.

Since a magnetic field is produced around a current-carrying conductor, such a field can be changed by changing the current. If the conductor in which an EMF is to be induced is part of an electric circuit, the induction can be caused by changing the current in that circuit; this is called self-induction. The induced EMF is always such that it opposes the change that gives rise to it, according to Lenz's law.

Changing the current in a given circuit can also induce an EMF in another nearby circuit, one that is unconnected with the original. This type of electromagnetic induction is called mutual induction and is the basis of the transformer plus a common cause of anomalies in aircraft systems. Electrostatic induction results when an unbalanced electric charge on a previously uncharged metallic body is a result of a charged object being brought near without touching. If the charged device is positive, electrons in the uncharged body will be attracted toward it; if the opposite end of the body is then grounded, electrons will flow onto it to replace those drawn to the other end, the body thus acquiring a negative charge after the ground connection is broken.

A similar procedure can be used to produce a positive charge on the uncharged body when a negatively charged device is brought near it. Magnetic induction is the production of a magnetic field in a piece of unmagnetized iron or other ferrous substance when a magnet is near. The magnet causes the individual particles of the iron, which act like tiny magnets, to line up so that the sample as a whole becomes magnetized. Most of this induced magnetism is lost when the magnet causing it is taken away.

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