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electrodynamic damping (electrical meter damping). The decreasing amplitude of pointer oscillation of
an electrical meter, caused by the generation of a voltage in the moving coil as it oscillates back and forth
in the field of a permanent magnet. Energy used to produce current in the moving coil decreases the energy
causing the oscillations.
electrodynamics. The aspect of electricity that deals with electrons in motion. This includes the effects of
magnetism and induction. The other aspect of electricity is electrostatics, which deals with electrical
charges caused by electrons that are stationary.
electrogalvanizing. The process of electrolytically depositing a layer of zinc on sheets of steel.
electroluminescence. The emission of light caused by the application of a strong electrical field to certain
materials. It is not caused by the heating effect of the electricity.
electrolysis. The process in which the chemical composition of a material is changed by passing electrical
current through it. When DC electricity passes through water, the water breaks down into its two chemical
constituents, hydrogen and oxygen. Hydrogen bubbles form on the negative electrode, and oxygen bubbles
form on the positive electrode.
electrolyte. A chemical solution, either a liquid or a gas, that conducts electrical current by releasing ions
(unbalanced atoms) that unite with oppositely charged ions on the electrodes. Negative ions, atoms having
an excess of electrons, move through the electrolyte to the positive electrode. Positive ions, atoms having a
deficiency of electrons, move to the negative electrode.
A lead-acid battery uses an electrolyte of sulfuric acid and water. When the battery is being
charged, negative sulfate ions from the plates join positive hydrogen ions in the water and form sulfuric
acid. When the battery discharges, negative sulfate ions leave the electrolyte and go to both plates. Positive
hydrogen ions left from the sulfuric acid join negative oxygen ions from the positive plate and form water.
The condition of charge of a lead-acid battery can be determined by measuring the specific gravity
of the electrolyte with a hydrometer. The specific gravity shows the amount of acid in the electrolyte.
electrolytic capacitor. A capacitor that uses metal foil for the electrodes and an extremely thin film of
metallic oxide, a nonconductor, as the dielectric. Two sheets of metal foil separated by a piece of porous
paper impregnated with an electrolyte are the plates. The dielectric is an oxide film formed on the surface
of one of the plates.
The capacity of a capacitor is inversely proportional to the thickness of the dielectric — the
thinner the dielectric, the greater the capacity. And, since the oxide film is extremely thin, an electrolytic
capacitor has a large capacity for its physical size.
One major disadvantage of an electrolytic capacitor is its low DC working voltage compared with
that of other types of capacitors. The thin oxide film can be easily punctured by a high voltage. An oxide
film on a piece of metal acts as a rectifier. Electrons can pass from the metal through the film into the
electrolyte. But they cannot pass from the electrolyte through the film to the metal.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 219
Because of this rectifying action, electrolytic capacitors must never be used in AC circuits, and
they must be installed in a DC circuit with their anode, the terminal marked with a plus sign, connected to
the positive voltage.
electrolytic dissociation. The reduction of certain chemical compounds into their composite elements by
passing electricity through them. When electrical current passes through water, it dissociates into hydrogen
and oxygen.
electromagnet. A magnet produced by electrical current flowing through a coil of wire. The coil of an
electromagnet is normally wound around a core of soft iron. This soft iron has an extremely low retentivity
so it releases the material being picked up as soon as current stops flowing through the coil.
electromagnetic emission (electronic communications). The radiation of electromagnetic energy for
communications. There are six types of amplitude-modulated emission classified by international
agreement. These are:
A0. Unmodulated continuous-wave
A1. Telegraphy, or pure continuous wave
A2. Modulated telegraphy
A3. Telephony
A4. Facsimile
A5. Television
electromagnetic induction. The transfer of electrical energy from one conductor to another that is not
electrically connected. This transfer is done by a changing magnetic field produced by current flowing in
one conductor cutting across the other conductor. As the lines of flux expand and collapse across the
　
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