The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 117. CHARACTERISTIC CURVE OF ALTERNATING CURRENT.
160 STANDARD ELECTRICAL DICTIONARY.
Current, Atomic.
A unit of current strength used in Germany; the strength of a current
which will liberate in 24 hours (86,400 seconds) one gram of hydrogen
gas, in a water voltameter. The atomic current is equal to 1.111
amperes. In telegraphic work the milliatom is used as a unit, comparable
to the milliampere. The latter is now displacing it.
Current, Charge.
If the external coatings of a charged and uncharged jar are placed in
connection, and if the inner coatings are now connected, after
separating them they are both found to be charged in the same manner. In
this process a current has been produced between the outside coatings
and one between the inner ones, to which Dove has given the name Charge
Current, and which has all the properties of the ordinary discharge
current. (Ganot.)
Current, Circular.
A current passing through a circular conductor; a current whose path is
in the shape of a circle.
Current, Commuted.
A current changed, as regards direction or directions, by a commutator,
q. v., or its equivalent.
Current, Constant.
An unvarying current. A constant current system is one maintaining such
a current. In electric series, incandescent lighting, a constant current
is employed, and the system is termed as above. In arc lighting systems,
the constant current series arrangement is almost universal.
161 STANDARD ELECTRICAL DICTIONARY.
Current, Continuous.
A current of one direction only; the reverse of an alternating current.
(See Current, Alternating.)
Current, Critical.
The current produced by a dynamo at its critical speed; at that speed
when a slight difference in speed produces a great difference in
electro-motive force. On the characteristic curve it corresponds to the
point where the curve bends sharply, and where the electro-motive force
is about two-thirds its maximum.
Current, Daniell/U.S. , Daniell/Siemens' Unit.
A unit of current strength used in Germany. It is the strength of a
current produced by one Daniell cell in a circuit of the resistance of
one Siemens' unit. The current deposits 1.38 grams of copper per hour.
It is equal to 1.16 amperes.
Current, Demarcation.
In electro-therapeutics, a current which can be taken from an injured
muscle, the injured portion acting electro-negatively toward the
uninjured portion.
Current Density.
The current intensity per unit of cross-sectional area of the conductor.
The expression is more generally used for electrolytic conduction, where
the current-density is referred to the mean facing areas of the
electrodes, or else to the facing area of the cathode only.
The quality of the deposited metal is intimately related to the current
density. (See Burning.)
Proper Current Density for Electroplating
Amperes Per Square Foot of Cathode.--(Urquhart.)
Copper, Acid Bath. 5.0 to 10.0
" Cyanide Bath, 3.0 " 5.0
Silver, Double Cyanide, 2.0 " 5.0
Gold, Chloride dissolved in Potassium Cyanide, 1.0 " 2.0
Nickel, Double Sulphate, 6.6 " 8.0
Brass, Cyanide, 2.0 " 3.0
Current, Diacritical.
A current, which, passing through a helix surrounding an iron core,
brings it to one-half its magnetic saturation, q. v.
Current, Diaphragm.
If a liquid is forced through a diaphragm, a potential difference
between the liquid on opposite sides of the diaphragm is maintained.
Electrodes or terminals of platinum may be immersed in the liquid, and a
continuous current, termed a diaphragm current, may be taken as long as
the liquid is forced through the diaphragm. The potential difference is
proportional to the pressure, and also depends on the nature of the
diaphragm and on the liquid.
162 STANDARD ELECTRICAL DICTIONARY.
Current, Direct.
A current of unvarying direction, as distinguished from an alternating
current. It may be pulsatory or intermittent in character, but must be
of constant direction.
Current, Direct Induced.
On breaking a circuit, if it is susceptible of exercising
self-induction, q. v., an extra current, in the direction of the
original is induced, which is called "direct" because in the same
direction as the original. The same is produced by a current in one
circuit upon a parallel one altogether separated from it. (See
Induction, Electro-Magnetic-Current, Extra.)
Synonym--Break Induced Current.
Current, Direction of.
The assumed direction of a current is from positively charged electrode
to negatively charged one; in a galvanic battery from the carbon or
copper plate through the outer circuit to the zinc plate and back
through the electrolyte to the carbon or copper plate. (See Current.)
[Transcriber's note: Current is caused by the motion of negative
electrons, from the negative pole to the positive. The electron was
discovered five years after this publication.]
Current, Displacement.
The movement or current of electricity taking place in a dielectric
during displacement. It is theoretical only and can only be assumed to
be of infinitely short duration. (See Displacement, Electric.)
Currents, Eddy Displacement.
The analogues of Foucault currents, hypothetically produced in the mass
of a dielectric by the separation of the electricity or by its
electrification. (See Displacement.)
Current, Extra.
When a circuit is suddenly opened or closed a current of very brief
duration, in the first case in the same direction, in the other case in
the opposite direction, is produced, which exceeds the ordinary current
in intensity. A high potential difference is produced for an instant
only. These are called extra currents. As they are produced by
electro-magnetic induction, anything which strengthens the field of
force increases the potential difference to which they are due. Thus the
wire may be wound in a coil around an iron core, in which case the extra
currents may be very strong. (See Induction, Self-Coil, Spark.)
Current, Faradic.
A term in medical electricity for the induced or secondary alternating
current, produced by comparatively high electro-motive force, such as
given by an induction coil or magneto-generator, as distinguished from
the regular battery current.
163 STANDARD ELECTRICAL DICTIONARY.
Current, Foucault.
A current produced in solid conductors, and which is converted into heat
(Ganot). These currents are produced by moving the conductors through a
field, or by altering the strength of a field in which they are
contained. They are the source of much loss of energy and other
derangement in dynamos and motors, and to avoid them the armature cores
are laminated, the plane of the laminations being parallel to the lines
of force. (See Core, Laminated.)
The presence of Foucault currents, if of long duration, is shown by the
heating of the metal in which they are produced. In dynamo armatures
they are produced sometimes in the metal of the windings, especially if
the latter are of large diameter.
Synonyms--Eddy Currents--Local Currents--Parasitical Currents.
Current, Franklinic.
In electro-therapeutics the current produced by a frictional electric
machine.
Current, Induced.
The current produced in a conductor by varying the conditions of a field
of force in which it is placed; a current produced by induction.
Current Induction.
Induction by one current on another or by a portion of a current on
another portion of itself. (See Induction.)
Current Intensity.
Current strength, dependent on or defined by the quantity of electricity
passed by such current in a given time. The practical unit of current
intensity is the ampere, equal to one coulomb of quantity per second of
time.
Current, Inverse Induced.
The current induced in a conductor, when in a parallel conductor or in
one having a parallel component a current is started, or is increased in
strength. It is opposite in direction to the inducing current and hence
is termed inverse. (See Induction, Electro-magnetic.) The parallel
conductors may be in one circuit or in two separate circuits.
Synonyms--Make-induced Current--Reverse-induced Current.
Current, Jacobi's Unit of.
A current which will liberate one cubic centimeter of mixed gases
(hydrogen and oxygen) in a water voltameter per minute, the gases being
measured at 0º C. (32º F.) and 760 mm. (29.92 inches) barometric
pressure. It is equal to .0961 ampere.
Current, Joint.
The current given by several sources acting together. Properly, it
should be restricted to sources connected in series, thus if two battery
cells are connected in series the current they maintain is their joint
current.
Current, Linear.
A current passing through a straight conductor; a current whose path
follows a straight line.
164 STANDARD ELECTRICAL DICTIONARY.
Current, Make and Break.
A succession of currents of short duration, separated by absolute
cessation of current. Such current is produced by a telegraph key, or by
a microphone badly adjusted, so that the circuit is broken at intervals.
The U. S. Courts have virtually decided that the telephone operates by
the undulatory currents, and not by a make and break current. Many
attempts have been made to produce a telephone operating by a
demonstrable make and break current, on account of the above
distinction, in hopes of producing a telephone outside of the scope of
the Bell telephone patent.
[Transcriber's note: Contemporary long distance telephone service is
digital, as this item describes.]
Current-meter.
An apparatus for indicating the strength of current. (See Ammeter.)
Current, Negative.
In the single needle telegraph system the current which deflects the
needle to the left.
Current, Nerve and Muscle.
A current of electricity yielded by nerves or muscles. Under proper
conditions feeble currents can be taken from nerves, as the same can be
taken from muscles.
Current, Opposed.
The current given by two or more sources connected in opposition to each
other. Thus a two volt and a one volt battery may be connected in
opposition, giving a net voltage of only one volt, and a current due to
such net voltage.
Current, Partial.
A divided or branch current. A current which goes through a single
conductor to a point where one or more other conductors join it in
parallel, and then divides itself between the several conductors, which
must join further on, produces partial currents. It produces as many
partial currents as the conductors among which it divides. The point of
division is termed the point of derivation.
Synonym--Derived Current.
Current, Polarizing.
In electro-therapeutics, a constant current.
Current, Positive.
In the single needle telegraph system the current which deflects the
needle to the right.
Current, Pulsatory.
A current of constant direction, but whose strength is constantly
varying, so that it is a series of pulsations of current instead of a
steady flow.
Current, Rectified.
A typical alternating current is represented by a sine curve, whose
undulations extend above and below the zero line. If by a simple two
member commutator the currents are caused to go in one direction, in
place of the sine curve a series of short convex curves following one
another and all the same side of the zero line results. The currents all
in the same direction, become what is known as a pulsating current.
Synonym--Redressed Current.
165 STANDARD ELECTRICAL DICTIONARY.
Current, Rectilinear.
A current flowing through a rectilinear conductor. The action of
currents depending on their distance from the points where they act,
their contour is a controlling factor. This contour is determined by the
conductors through which they flow.
Current Reverser.
A switch or other contrivance for reversing the direction of a
current in a conductor.
Currents, Ampérian.
The currents of electricity assumed by Ampere's theory to circulate
around a magnet. As they represent the maintenance of a current or of
currents without the expenditure of energy they are often assumed to be
of molecular dimensions. As they all go in the same sense of rotation
and are parallel to each other the result is the same as if a single set
of currents circulated around the body of the magnet. More will be found
on this subject under Magnetism. The Ampérian currents are purely
hypothetical and are predicated on the existence of a field of force
about a permanent magnet. (See Magnetism, Ampére's Theory of.)
If the observer faces the north pole of a magnet the Ampérian currents
are assumed to go in the direction opposite to that of a watch, and the
reverse for the south pole.

Figs. 118-119 DIRECTION OF AMPÉRIAN CURRENTS.
Currents, Angular.
Currents passing through conductors which form an angle with each other.
Currents, Angular, Laws of.
1. Two rectilinear currents, the directions of which form an angle with
each other, attract one another when both approach to or recede from the
apex of the angle.
2. They repel one another, if one approaches and the other recedes from
the apex of the angle.
166 STANDARD ELECTRICAL DICTIONARY
Currents, Earth.
In long telegraph lines having terminal grounds or connected to earth
only at their ends, potential differences are sometimes observed that
are sufficient to interfere with their working and which, of course, can
produce currents. These are termed earth-currents. It will be noted that
they exist in the wire, not in the earth. They may be of 40 milliamperes
strength, quite enough to work a telegraph line without any battery.
Lines running N. E. and S. W. are most affected; those running N.W. and
S. E. very much less so. These currents only exist in lines grounded at
both ends, and appear in underground wires. Hence they are not
attributable to atmospheric electricity. According to Wilde they are the
primary cause of magnetic storms, q. v., but not of the periodical
changes in the magnetic elements. (See Magnetic Elements.)
Synonym--Natural Currents.
Current, Secondary.
(a) A current induced in one conductor by a variation in the current in
a neighboring one; the current produced in the secondary circuit of an
induction coil or alternating current converter.
(b) The current given by a secondary battery. This terminology is not to
be recommended.
Current, Secretion.
In electro-therapeutics, a current due to stimulation of the secretory
nerves.
Current Sheet.
(a) If two terminals of an active circuit are connected to two points of
a thin metallic plate the current spreads over or occupies practically a
considerable area of such plate, and this portion of the current is a
current sheet.
The general contour of the current sheet can be laid out in lines of
flux. Such lines resemble lines of force. Like the latter, they are
purely an assumption, as the current is not in any sense composed of
lines.
(b) A condition of current theoretically brought about by the Ampérian
currents in a magnet. Each molecule having its own current, the
contiguous portions of the molecules counteract each other and give a
resultant zero current. All that remains is the outer sheet of electric
current that surrounds the whole.
Current, Sinuous.
A current passing through a sinuous conductor.
Currents, Multiphase.
A term applied to groups of currents of alternating type which
constantly differ from each other by a constant proportion of periods of
alternation. They are produced on a single dynamo, the winding being so
contrived that two, three or more currents differing a constant amount
in phase are collected from corresponding contact rings. There are
virtually as many windings on the armature as there are currents to be
produced. Separate conductors for the currents must be used throughout.
Synonyms--Polyphase Currents--Rotatory Currents.
167 STANDARD ELECTRICAL DICTIONARY.
Currents of Motion.
In electro-therapeutics, the currents produced in living muscle or
nerves after sudden contraction or relaxation.
Currents of Rest.
In electro-therapeutics, the currents traversing muscular or nervous
tissue when at rest. Their existence is disputed.
Currents, Orders of.
An intermittent current passing through a conductor will induce
secondary alternating currents in a closed circuit near it. This
secondary current will induce a tertiary current in a third closed
circuit near it, and so on. The induced currents are termed as of the
first, second, third and other orders. The experiment is carried out by
Henry's coils. (See Coils, Henry's.)
Currents, Thermo-electric.
These currents, as produced from existing thermo-electric batteries,
are generated by low potential, and are of great constancy. The opposite
junctions of the plates can be kept at constant temperatures, as by
melting ice and condensing steam, so that an identical current can be
reproduced at will from a thermopile.
Thermo-electric currents were used by Ohm in establishing his law. (See
Ohm's Law.)
Current, Swelling.
In electro-therapeutics, a current gradually increasing in strength.
Current, Undulatory.
A current varying in strength without any abrupt transition from action
to inaction, as in the make and break current. The current may be
continually changing in direction (see Current, Alternating), and hence,
of necessity, may pass through stages of zero intensity, but such
transition must be by a graduation, not by an abrupt transition. Such
current may be represented by a curve, such as the curve of sines. It is
evident that the current may pass through the zero point as it crosses
the line or changes direction without being a make and break current.
When such a current does alternate in direction it is sometimes called a
"shuttle current." The ordinary commercial telephone current and the
alternating current is of this type. (See Current, Make and Break.)
Current, Unit.
Unit current is one which in a wire of unit length, bent so as to form
an arc of a circle of unit length of radius, would act upon a unit pole
(see Magnetic Pole, Unit,) at the center of the circle with unit force.
Unit length is the centimeter; unit force is the dyne.
[Transcriber's note: The SI definition of an ampere: A current in two
straight parallel conductors of infinite length and negligible
cross-section, 1 metre apart in vacuum, would produce a force equal to
2E-7 newton per metre of length.]
168 STANDARD ELECTRICAL DICTIONARY.
Current, Wattless.
Whenever there is a great difference in phase in an alternating current
dynamo between volts and current, the true watts are much less than the
product of the virtual volts and amperes, because the the watts are
obtained by multiplying the product of the virtual volts and amperes by
the cosine of the angle of lag (or lead). Any alternating current may be
resolved into two components in quadrature with each other, one in phase
with the volts, the other in quadrature therewith, the former is termed
by S. P. Thompson the Working Current, the latter the Wattless Current.
The greater the angle of lag the greater will be the wattless current.
Curve, Arrival.
A curve representing the rate of rise of intensity of current at the end
of a long conductor when the circuit has been closed at the other end.
In the Atlantic cable, for instance, it would require about 108 seconds
for the current at the distant end to attain 9/10 of its full value. The
curve is drawn with its abscissa representing time and its ordinates
current strength.
Curve, Characteristic.
A curve indicating, graphically, the relations between any two factors,
which are interdependent, or which vary simultaneously. Thus in a
dynamo, the voltage increases with the speed of rotation, and a
characteristic curve may be based on the relations between the speed of
rotation and voltage developed. The current produced by a dynamo varies
with the electro-motive force, and a curve can express the relations
between the electro-motive force and the current produced.
A characteristic curve is usually laid out by rectangular co-ordinates
(see Co-ordinates). Two lines are drawn at right angles to each other,
one vertical, and the other horizontal. One set of data are marked off
on the horizontal line, say one ampere, two amperes, and so on, in the
case of a dynamo's characteristic curve.
For each amperage of current there is a corresponding voltage in the
circuit. Therefore on each ampere mark a vertical is erected, and on
that the voltage corresponding to such amperage is laid off. This gives
a series of points, and these points may be connected by a curve. Such
curve will be a characteristic curve.
The more usual way of laying out a curve is to work directly upon the
two axes. On one is laid off the series of values of one set of data; on
the other the corresponding series of values of the other dependent
data. Vertical lines or ordinates, q. v., are erected on the horizontal
line or axis of abscissas at the points laid off; horizontal lines or
abscissas, q. v., are drawn from the points laid off on the vertical
line or axis of ordinates. The characteristic curve is determined by the
intersections of each corresponding pair of abscissa and ordinate.
169 STANDARD ELECTRICAL DICTIONARY.
Variations exist in characteristic curve methods. Thus to get the
characteristic of a commutator, radial lines may be drawn from a circle
representing its perimeter. Such lines may be of length proportional to
the voltage developed on the commutator at the points whence the lines
start. A cut giving an example of such a curve is given in Fig. 125.
(See Curve of Distribution of Potential in Armature.)
There is nothing absolute in the use of ordinates or abscissas. They may
be interchanged. Ordinarily voltages are laid off as ordinates, but the
practise may be reversed. The same liberty holds good for all
characteristic curves. Custom, however, should be followed.
Synonym--Characteristic.

Fig. 120. CHARACTERISTIC CURVE OF A DYNAMO
WITH HORSE POWER CURVES.
Curve, Characteristic, of Converter.
The characteristic curve of the secondary circuit of an alternating
current converter. It gives by the usual methods (see Curve,
Characteristic,) the relations between the electro-motive force and the
current in the secondary circuit at a fixed resistance. If connected in
parallel a constant electro-motive force is maintained, and the curve is
virtually a straight line. If connected in series an elliptical curve is
produced.
170 STANDARD ELECTRICAL DICTIONARY.
Curve, Charging.
In secondary battery manipulation, a curve indicating the increase of
voltage as the charging is prolonged. The rise in voltage with the
duration of the charging current is not uniform. In one case, shown in
the cut, there was a brief rapid rise of about 0.1 volt; then a long
slow rise for 0.15 volt; then a more rapid rise for nearly 0.40 volt,
and then the curve became a horizontal line indicating a cessation of
increase of voltage. The charging rate should be constant.
The horizontal line is laid off in hours, the vertical in volts, so that
the time is represented by abscissas and the voltage by ordinates of the
curve.

Fig. 121. CHARGING CURVE OF A SECONDARY BATTERY.
Curve, Discharging.
A characteristic curve of a storage battery, indicating the fall in
voltage with hours of discharge. The volts may be laid off on the axis
of ordinates, and the hours of discharging on the axis of abscissas. To
give it meaning the rate of discharge must be constant.
Curve, Electro-motive Force.
A characteristic curve of a dynamo. It expresses the relation between
its entire electromotive force, as calculated by Ohm's Law, and the
current intensities corresponding thereto. To obtain the data the dynamo
is driven with different resistances in the external circuit and the
current is measured for each resistance. This gives the amperes. The
total resistance of the circuit, including that of the dynamo, is known.
By Ohm's Law the electro-motive force in volts is obtained for each case
by multiplying the total resistance of the circuit in ohms by the
amperes of current forced through such resistance. Taking the voltages
thus calculated for ordinates and the corresponding amperages for
abscissas the curve is plotted. An example is shown in the cut.
171 STANDARD ELECTRICAL DICTIONARY.
Curve, External Characteristic.
A characteristic curve of a dynamo, corresponding to the electro-motive
force curve, except that the ordinates represent the voltages of the
external circuit, the voltages as taken directly from the terminals of
the machine, instead of the total electro-motive force of the circuit.
The dynamo is run at constant speed. The resistance of the external
circuit is varied. The voltages at the terminals of the machine and the
amperages of current corresponding thereto are determined. Using the
voltages thus determined as ordinates and the corresponding amperages as
abscissas the external characteristic curve is plotted.
This curve can be mechanically produced. A pencil may be moved against a
constant force by two electro-magnets pulling at right angles to each
other. One must be excited by the main current of the machine, the other
by a shunt current from the terminals of the machine. The point of the
pencil will describe the curve.

Fig. 122. CHARACTERISTIC CURVE OF A DYNAMO.
Curve, Horse Power.
Curves indicating electric horse power. They are laid out with
co-ordinates, volts being laid off on the axis of ordinates, and amperes
on the axis of abscissas generally. The curves are drawn through points
where the product of amperes by volts equals 746. On the same diagram 1,
2, 3 .... and any other horse powers can be plotted if within the
limits. See Fig. 120.
Curve, Isochasmen.
A line drawn on the map of the earth's surface indicating the locus of
equal frequency of auroras.
172 STANDARD ELECTRICAL DICTIONARY.
Curve, Life.
A characteristic curve showing the relations between the durability and
conditions affecting the same in any appliance. It is used most for
incandescent lamps. The hours of burning before failure give ordinates,
and the rates of burning, expressed indirectly in volts or in
candle-power, give abscissas. For each voltage or for each candle-power
an average duration is deducible from experience, so that two dependent
sets of data are obtained for the construction of the curve.
Curve, Load.
A characteristic curve of a dynamo, expressing the relation between its
voltage and the amount of excitation under a definite condition of
ampere load, at a constant speed. The ordinates represent voltage, the
abscissas ampere turns in the field, and the curves may be constructed
for a flow of 0, 50, 100, or .. , or any other number of amperes.