AMC (automatic mixture control). The device in a fuel metering system such as a carburetor or fuel
injection system that keeps the fuel-air mixture ratio constant as the density of the air changes with altitude. American Standards. Dimensional standards for fasteners issued by the American Standards Association (ASA).
American Wire Gage. See AWG. americium. A chemical element in the actinide series. The symbol for americium is Am, its atomic number is 95, and the mass number of its isotope
having the longest half life is 243.
ammeter. An instrument installed in series with an electrical load to measure the amount of current flowing through the load.
Ammeters which measure very small rates of flow are called milliammeters (thousandths of an ampere) and microammeters (millionths of an ampere).
ammeter shunt. A low-resistance precision resistor installed in parallel with an ammeter between a source of electrical energy and an electrical load to allow the meter to read a flow of current which exceeds the limit of the instrument.
Most of the current in the circuit flows through the shunt and produces a voltage drop. The ammeter, acting as a millivoltmeter, measures the voltage drop across the shunt and indicates, on a special scale, the amount of current flowing through the circuit.

ammonia. A pungent, invisible gas made up of one atom of nitrogen and three atoms of hydrogen (NH3). Ammonia becomes a liquid at -28°F and freezes at -107.6°F.
Ammonia is used to case harden steel by the nitriding process. In this process, the ammonia combines with aluminum, which has been alloyed with the steel, to form aluminum nitride. Aluminum nitride gives the steel a very hard surface.
amorphous. Without shape (“a” means without, and “morphous” means shape) or without a definite character or nature.
Clay is a form of amorphous soil, but sand, which is made of crystals, is not amorphous. The crystals have a definite shape.
ampere (A). A measure of electron (current) flow. One ampere is equal to a flow of one coulomb (6.28 billion billion electrons) past a point in one second.
One ampere is also the amount of current that can be forced through one ohm of resistance by a pressure of one volt. See coulomb.
ampere-hour. The quantity of electricity that passes through a circuit when one ampere flows for one hour.
ampere-hour capacity. A rating that indicates the amount of electrical energy a battery can supply. The ampere-hour rating is the product of the current flow in amperes, multiplied by the length of time, in hours, the battery can supply this current. A 35-ampere-hour battery can supply seven amperes of current for five hours, or one ampere for 35 hours.
ampere-hour meter. An electrical meter that measures the amount of current per unit of time used in a circuit.
ampere-turn. A measure of magnetomotive force (mmf) of an electromagnet. One ampere turn is the amount of mmf produced when one ampere of current flows through one turn of wire in a coil. One ampere turn is equal to 1.26 gilberts.