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Contents. • U.S. Government Printing Office; 1945 - 618779
APPENDIX TABLE I
- AGONIC: An imaginary line of the earth's surface passing through points where the magnetic declination is
0°, that is, points where the compass points true north.
- ALTERNATOR: An alternating current generator. AMMETER: The instrument for the measurement of current.
- AMPERE: The unit of electrical current.
- AMPERE-HOUR: The quantity of electricity equivalent to a current of one ampere flowing past a point in a
conductor in one hour.
- AMPERE-TURN: The magnetizing force produced by a current of one ampere flowing through a coil of one turn.
- ANODE: The electrode in a cell (voltaic or electrolytic) that attracts the negative ions and repels the
positive; the positive pole.
- ARC: The luminous glow between incandescent electrodes.
- ARMATURE: The movable part of a motor or the removable part of a magnetic circuit, such as the iron placed
across the poles of a horseshoe magnet.
- AUTO-TRANSFORMER: A transformer in which the primary and secondary are connected together in one winding.
- BATTERY: A. group of several cells connected together as a unit.
- BRANCH CIRCUIT: One of the conductors in a parallel circuit.
- BRUSH: The conducting material, usually a block of carbon, bearing against the commutator or slip-rings
through which the current flows in or out.
- CATHODE: The electrode in a cell (voltaic or primary) that attracts the positive ions and repels the
negative ions; the negative pole.
- CHOKE COIL: A coil of low ohmic resistance and comparatively high impedance to alternating current.
- -CIRCUIT: The complete path of an electric current including, usually, the generating device.
- CIRCUIT BREAKER: A device that opens a circuit while it is carrying current; often used in abnormal
conditions, such as overloads.
- CIRCULAR MIL: An area equal to that of a circle with a diameter of 0.001 inch. It is used for measuring the
cross section of wires.
- COMMUTATOR: That part of the armature of a dynamo which converts an alternating into a direct current.
- CONDENSER: A device consisting of two or more conductors separated by non-conductor material; it holds or
stores an electric charge.
- CONDUCTANCE: The reciprocal of electrical resistance. Conducting power.
- CONDUCTIVITY: The ease with which a substance transmits electricity.
- CONDUCTOR: A material capable of transmitting electric current.
- CONVERTER, ROTARY: An electrical machine having a commutator at one end and slip-rings at the other end of
the armature. It is used for the conversion of alternating to direct current.
- CORE: A mass of iron placed inside a coil to increase its magnetism.
- COULOMB: The-unit of static electricity; the quantity of electricity transferred by one ampere in one
- COUNTER EMF: Counter electromotive force; an EMF induced in a coil or armature that opposes the applied
- CURRENT OF ELECTRICITY: The continuous flow of electrons in a circuit.
- D'ARSONVAL GALVANOMETER: A galvanometer in which a moving coil swings between the poles of a permanent
- DEMAGNETIZE: To deprive a body of its magnetic properties.
- DIELECTRIC: A non-conducting material.
- DIODE: A vacuum tube containing the filament and the plate; it serves as a rectifier of alternating current.
- DIP NEEDLE: A magnetized needle capable of rotation in a vertical plane.
- DIRECT CURRENT: An electric current that flows in one direction only.
- DYNAMO: A machine for converting mechanical energy into electrical energy or vice versa.
- EDDY CURRENT: A current induced in the core of an armature of a motor, dynamo, or transformer caused by
changes in the magnetic field.
- EFFICIENCY: The ratio of a machine's useful work output to the total input.
- ELECTRODE: The terminal by which current leaves or enters an electrolytic cell.
- ELECTROLYTE: A substance that conducts a current by the movement of ions.
- ELECTROMAGNET: A magnet made by passing current through a coil of wire wound on a soft iron core.
- ELECTROMOTIVE FORCE (EMF): The electrical force that moves or tends to move electrons; ELECTRON: The
smallest particle of negative electricity.
- ELECTROPLATING: The electrical method of plating a surface with a metal.
- ENERGY: The ability or capacity to do work.
- FIELD: The region where a magnet or electrical charge is capable of exerting its force.
- FIELD COIL: One of the coils used to excite a field magnet.
- FIELD MAGNET: The magnet used to produce a magnetic field (usually in motors or generators).
- FLUX: Magnetic lines of force, assumed to flow from the north pole to the south pole of a magnet.
- FREQUENCY: The number of cycles of an alternating current per second.
- FUSE: A part of a circuit made of a material that will melt and break the circuit when current is increased
beyond a specific value.
- GALVANOMETER: An instrument used to measure small currents.
- GENERATOR: A machine that converts mechanical energy into electrical energy.
- GRID: A metal wire mesh placed between the cathode and plate.
- GRID BATTERY: The battery used to supply the desired potential to the grid.
- GRID LEAK: A very high resistance placed in parallel with the grid condenser.
- GROUND: A connection made directly to the earth or to a frame or structure which serves as one line of a
- HORSEPOWER: The English unit of power, equal to work done at the rate of 550 foot-pounds per second. Equal
to 746 watts of electrical power.
- INDUCE: To produce an effect in a body by exposing it to the influence-of a magnetic force, an electric
force, or a changing current.
- INDUCTION COIL: Two coils so arranged that an interrupted current in the first produces a voltage in the
- INTERRUPTER: A device for the automatic making and breaking of an electrical circuit.
- ION: An electrically charged atom.
- ISOGONIC LINE: An imaginary line drawn through points on the earth's surface where the magnetic deviation is
- JOULE: A unit of energy or work. A joule of energy is liberated by one ampere flowing for one second through
a resistance of one ohm.
- LAG: The number of degrees an alternating current lags behind voltage.
- LAMINATIONS: The thin sheets or discs making up an iron core.
- LEYDEN JAR: An early form of condenser.
- LINE OF FORCE: A line in a field of force that shows the direction of the force.
- LOAD: The energy delivered by a generator to its circuit.
- LODESTONE: A piece of magnetite.
- MAGNETIC CIRCUIT: The complete path followed by magnetic lines of force.
- MAGNETIC FLUX: The total number of lines of force issuing from a pole.
- MAGNETITE: An iron ore that is magnetic.
- MAGNETO: A generator in which the field is sup- plied by a permanent magnet.
- MEGOHM: A million ohms.
- MIL: One thousandth of an inch.
- MILLIAMMETER: An ammeter reading thousandths of an ampere.
- MILLIVOLTMETER: A voltmeter reading thousandths of a volt.
- MOTOR-GENERATOR (M-G): A generator driven by an electric motor.
- MUTUAL INDUCTION: The inducing of an EMF in a circuit by the field of a nearby circuit.
- NEGATIVE CHARGE: The electrical charge carried by a body which has an excess of electrons. (For example, a
vulcanic rod, after it has been rubbed by fur or wool, carries a negative charge.)
- NEUTRON: A particle having the weight of a pro-ton but carrying no electric charge.
- NUCLEUS: The heavy or central part of an atom. OHMMETER: An instrument for directly measuring ohms.
- PERMALLOY: An alloy containing 78.5 percent nickel and 21.5 percent iron. It has an abnormally high magnetic
- PERMEABILITY: A property of matter that indicates the ease with which it is magnetized.
- PLATE CURRENT: The current that flows from the plate of a vacuum tube.
- POLARITY: The character of having magnetic poles, or electric charges.
- POLE: One of the ends of a magnet where most of its magnetism is concentrated.
- POSITIVE CHARGE: The electrical charge carried by a body which has become deficient in electrons. (For
example, a glass rod, after it has been rubbed by silk, carries a positive charge.)
- POTENTIAL: The amount of charge held by a body.
- POWER: The time rate of doing work.
- PROTON: A positively charged, particle whose charge is equal, but opposite, to that of the electron.
- RECTIFY: To change an alternating current to a unidirectional or direct current.
- RELAY: An electrically operated device for the closing and opening of a circuit.
- RELUCTANCE: A measure of the resistance of a material to magnetic lines of force.
- RESISTANCE: The opposition of a conductor to an electric current.
- RETENTIVITY: The property of retaining magnetism.
- SATURATION, MAGNETIC: The condition of a magnetic substance when its magnetism has reached its highest
- SELF INDUCTION: The process by which a circuit induces an EMF in itself by its own magnetic field.
- SERIES CONNECTION: An arrangement of cells, generators, condensers, or conductor each carries the entire
current of the circuit.
- SERIES-WOUND: Having the armature wired in series with the field winding. (Applied to motors or generators.)
- SOLENOID: A coil of wire used to produce a magnetic field.
- SPACE CHARGE: The charge acquired by the space inside a vacuum tube due to the presence of electrons.
- STEP-DOWN TRANSFORMER: A transformer with fewer turns in the secondary than in the primary.
- STEP-UP TRANSFORMER: A transformer with more turns in the secondary than in the primary.
- THERMOCOUPLE: A pair of metals which generate an EMF by the heating of one of the junctions; it is used to
measure temperature differences.
- TRANSFORMER: A device that, without moving parts, transfers electrical energy from one circuit to another
circuit by the aid of electromagnetic induction.
- TRIODE: A vacuum tube containing a filament, grid, and plate.
- UNIDIRECTIONAL: As applied to a current of electricity, a current that flows in one direction only.
- VACUUM TUBE: A tube from which the air has been pumped out. The tube contains an element that emits
electrons when properly excited and an electrode to attract the electrons and set up a current in an external
- VOLT: The practical unit of electrical pressure.
- WATT: A unit of power produced by a current of one ampere at one volt.
- WATTMETER: An instrument for measuring electric power in watts.
APPENDIX TABLE II
OHM'S LAW -
For voltage ............... E = IR
For current ............... I = E/R
resistance .......... R = E/I
POWER EQUATION -
For power ................ P = IE
P = I2R
P = E2/R
For current ............... I = P/E
For voltage .............. E = P/I
current .............. I = (Ea - Eg)/Ra
For IR drop .............. IR = Ea
Voltage-turns .......... Ep/Es = Tp/Ts
Current-turns .......... Ip/Is = Is/Ip
...................... IpEp = IsEs
Ampere-turns .......... IpTp = IsTs
SERIES CIRCUITS -
For voltage ............... Et = E1 + E2 + E3
For current ............... It = I1 = I2 = I3 ...
resistance .......... Rt
= R1 + R2 + R3 ...
PARALLEL CIRCUITS -
For voltage .............. Et
= E1 = E2 = E3 ...
For current .............. It = I1
+ I2 + I3 ...
For resistance ......... 1/Rt = 1/R1 + 1/R2
For hp ...................... hp = P/746
For watts ................. P = 746
¶ U.S. GOVERNMENT PRINTING OFFICE; 1945- 618779