Inductance

“ When an alternating current passes through a circuit, the action termed self-induction sets up an electromotive force in the circuit that opposes the flow of current, as does the resistance of the wire, and this is called the inductance of the circuit. ”

“ Inertia is that property of a material body that requires time and energy to set in motion, or stop. Inductance is that property of an oscillation circuit that makes an electric current take time to start and time to stop. Because of the inductance, when a current flows through a circuit it causes the electric energy to be absorbed and changes a large part of it into magnetic lines of force. Where high frequency currents surge in a circuit the inductance of it becomes a powerful factor. ”

“ The more turns there are included in the part of the coil which we are using the greater is the inductance. If we want to do a real job we can bring each of these taps to a little stud and arrange a sliding or rotating contact with them. ”

“ EXAMPLE.—An air core coil has an inductance of 50 milli-henrys; if an iron core, having a permeability of 600 be inserted, what is the inductance?
The inductance of the air core coil will be multiplied by the permeability of the iron ”

“ The capacity of an electrical circuit corresponds to the elastic pliability, or what is commonly called the elasticity, of a material substance, and the inductance to mass or inertia. Hence capacity and inductance are qualities of an electric circuit which are analogous to the elasticity and inertia of such a body as a heavy spring. ”

“ Inductance not only sets up a counter-electromotive force in the line, which reduces the voltage delivered to it by generators or transformers, but also causes a larger current to flow in the line than is indicated by the division of the number of watts delivered to it by the virtual voltage of delivery. ”

“ If there were two boys it would be four times as hard as for one boy. If there were four in the group it would be sixteen times, and if five it would be twenty-five times. The difficulty increases much more rapidly than the number of boys.
Now all we have to do to get the right idea of inductance 104is to think of each boy as standing for the electrons in one turn of the coil. If there are five turns there will be twenty-five times as much inductance, as for a single turn; and so on. You see that we can change the inductance of a coil very easily by changing the number of turns. ”

“ The effect of capacity in a circuit is to cause the current to rise to its maximum value sooner than it would otherwise do; capacity produces an effect exactly the opposite of inductance. The phase relation between current and pressure with current leading is shown graphically by the two armature positions in full and dotted lines, corresponding respectively to current and pressure at the beginning of the cycle. ”

“ It must not be supposed that this arrangement of lamps, etc. is a general one; it being adopted to suit certain special conditions.
The formula for inductance reactance is Xi = 2πfL, and for capacity reactance, Xc = 1 ÷ (2πfC) ; accordingly if capacity and inductance in a circuit be equal, that is, if the circuit be resonant
from which
Ques. ”

“ The influence of a coil of wire upon an alternating current passing through it, tending to choke or diminish the current, or the similar influence of a condenser; inductive resistance. Reactance is measured in ohms. The reactance of a circuit is equal to the component of the impressed electro-motive force at right angles to the current divided by the current, that is, the component of the impedance due to the self-inductance or capacity of the circuit. ”

“ Place your inductance coils into your telephone-line at such distances336 apart that for all vibratory motions of electricity which it is desirable to transmit there shall be several coils per wave-length. In telephonic transmission of speech that means one coil every four or five miles on overhead wires, and one coil in about every one to two miles in a telephone cable. For these wave-lengths, the wire possessing discreet lumps of inductance in the form of inductance-coils acts like a wire with uniformly distributed inductance. ”

“ It is a little difficult without the employment of mathematical analysis to explain precisely the manner in which earthing one side of the loop or making the loop unsymmetrical as regards inductance has the effect of creating overtones in it. The following rough illustration may, however, be of some assistance. Imagine a long spiral metallic spring supported horizontally by threads. Let this represent a conductor, and let any movement to or fro of a part of the spring represent a current in that conductor. ”

“ A diagram is unnecessary in obtaining the impressed pressure since it is simply the difference between inductance pressure and capacity pressure (the circuit being assumed to have no resistance) , that is
impressed pressure = Ei - Ec = 377 - 255 = 122 volts.
EXAMPLE.—A circuit in which a current of 20 amperes is flowing at a frequency of 100, has an inductance reactance of 18.25 ohms, and a capacity of 125 microfarads. What is the impedance? ”

“ Deptford, Eng., alternating current plant. It is observed that the
potential difference between the members of a pair of mains rises or
increases with the distance the place of trial is from the station.
[Transcriber's note: This effect is due to the voltage drop across the
line inductance (due to charging current) being in phase with the
sending end voltages. Both capacitance and inductance are responsible
for producing this phenomenon. The effect is more pronounced in
underground cables and with very light loads.]
252 STANDARD ELECTRICAL DICTIONARY.
Ferro-magnetic. ”

“ In all these investigations, in all these experiments, which are so very, very interesting, for many years past--ever since the greatest experimenter who lectured in this hall discovered its principle--we have had a steady companion, an appliance familiar to every one, a plaything once, a thing of momentous importance now--the induction coil. There is no dearer appliance to the electrician. From the ablest among you, I dare say, down to the inexperienced student, to your lecturer, we all have passed many delightful hours in experimenting with the induction coil. ”

“ If now a coil of insulated wire S be included in the circuit, Fig. 2, upon repeating the make and break of contact, [Pg 3] the sparks will be much increased. This arises from induction, each adjacent turn of wire acting upon its neighbor. To better understand the action of induction, we will consider the following examples: Fig. 3. A is a circuit in which is the battery cell B. C is a second circuit lying close to but well insulated from circuit A. G is a galvanometer in which a magnetized needle swings right or left each time a current is passed through a coil of wire encircling it. ”

“ The unit of self-induction is the same as that of induction in general.
It is the henry, q. v.
Induction, Unipolar.
Induction produced in a conductor which continuously cuts the lines of
force issuing from one pole of a magnet. As the lines of force are
always cut in the same sense a continuous and constant direction current
is produced. ”

“ To the terminals of an induction coil two metal spheres AA1
are connected as shown. This apparatus is termed the exciter; in its
discharge a series of isochronous discharges takes place, alternating in
direction. The period of duration T of a single one is given by the
formula T= 2* PI * squareRoot ( LC ) , in which C is the capacity and L
is the self-induction. The spheres may be 30 centimeters (11.8 inches)
in diameter, connected each to conductors 0.5 centimeter (.2 inch) in
diameter and 40 centimeters (15.7 inches) long each. ”

“ But as the induction-current close to the wire dies away, a new induction-current is generated in the medium beyond, so that the space occupied by the induction-current is continually becoming wider, while its intensity is continually diminishing. ”

“ To this power of propagation he gave the name 'specific inductive capacity.' He then glanced at conduction in its relation to induction, and generalised thus: 'Can we not, by a gradual chain of association, carry up the discharge from its occurrence in air through spermaceti and water to solutions, and then on to chlorides, oxides, and metals, without any essential change in its character?' The action of the particles of the best conductor differs, according to Faraday, only in degree from that of the particles of the insulator. ”

“ There are eight chapters which, starting with a general consideration of electrical induction, go on to a special consideration of the structure of the induction coil, its manipulation and care, the discharges in partial and high vacua, and finally spectrum work and X rays, which seem to cover the ground fairly well in an elementary way. ”

“ If the circuit be straight, there will be little self-induction, but if coiled, the effect will become pronounced. If the surrounding medium be air, the self-induction is small, but if it be iron, the self-induction is considerable.
Figs. 2,671 to 2,676.—The effect of self-induction. In a non-inductive circuit, as in fig. 2,672, the whole of the virtual pressure is available to cause current to flow through the lamp filament, hence it will glow with maximum brilliancy. If an inductive coil be inserted in the circuit as in fig. ”

“ Thus this induction disappears twice in
swinging a ship through a complete circle; deviation due to it is termed
semi-circular deviation. (See Deviation, Semi-circular.)
Fig. 202. INDUCTOR DYNAMO.
Inductophone.
A method of train telegraphy. The train carries a circuit including a
coil, and messages are picked up by it from coils along the line into
which an alternating current is passed. A telephone is used as a
receiver in place of a sounder or relay. The invention, never
practically used, is due to Willoughby Smith.
305 STANDARD ELECTRICAL DICTIONARY.
Inductor. ”

“ Since the inductors, in passing a north pole generate electromotive forces in one direction, and in passing a south pole generate electromotive forces in the opposite direction, it is evident that an inductor in one of these groups ought to be connected to one in nearly a corresponding position in the other group, so that the current may flow down one and up the other in agreement with the directions of the electromotive forces. ”

“ Ans. In order to induce an electromotive force by moving a conductor across a uniform magnetic field, it is necessary that the conductor, in its motion, should so cut the magnetic lines as to alter the number of lines of force that pass through the circuit of which the moving conductor forms a part.
Ques. What is the proper name for a “conductor” which moves across the magnetic field?
Ans. An inductor, because it is that part of the electric circuit in which induction takes place.
In the case of a dynamo, an inductor may be either a copper wire or copper bar.128
Ques. ”

“ If we call the reciprocal of the resistance of a conductor the conductivity of the conductor, then we may say that the conductivity of a multiple conductor is the sum of the conductivities of the component conductors. ”

“ But by putting the inductor in communication with the receiver , and the inductor with the receiver , the potentials of the inductors will be continually increased, and the quantity of electricity communicated to the receivers in each revolution will continually increase.
For instance, let the potential of and be , and that of and , , and when the carrier is within let the charge on and be , and that on the carrier , then, since the potential of the carrier is zero, being in contact with earth, its charge is . ”

“ Induction appears to consist in a certain polarized state of the particles, into which they are thrown by the electrified body sustaining the action, the particles assuming positive and negative points or parts, which are symmetrically arranged with respect to each other and the inducting surfaces or particles. The state must be a forced one, for it is originated and sustained only by force, and sinks to the normal or quiescent state when that force is removed. It can be continued only in insulators by the same portion of electricity, because they only can retain this state of the particles. ”

“ Electric Potential.—Suppose then that we have a conductor charged with electricity; we may imagine its surface to be divided up into small unequal areas, each of which carries a unit charge of electricity. If we consider lines of electric force to be drawn from the boundaries of these areas, they will cut up the space round the conductor into tubular surfaces called tubes of electric force, and each tube will spring from an area of the conductor carrying a unit electric charge. ”

“ Induction motors and other inductive apparatus take a component of current which lags behind the line pressure, and thereby lowers the power factor of the system, while a non-inductive load, such as incandescent lamps, takes only current in phase with the voltage and operates at unity power factor. ”

“ For relative
conducting power, tables of conductivity, q. v., should be consulted.
The metals beginning with silver are the best conductors, glass is one
of the worst.
[Transcriber's note: See "ether" for contemporary comments on this now
discarded concept.]
Conductor, Anti-Induction.
A current conductor arranged to avoid induction from other lines. Many
kinds have been invented and made the subject of patents. A fair
approximation may be attained by using a through metallic circuit and
twisting the wires composing it around each other. ”

“ Wet the ends of two fingers of the left hand, press one upon L and the other on R, thus making a shunt with your hand. With the right hand work the key rapidly. If the current is strong enough you should feel a slight shock in the fingers each time the circuit is broken. The extra current (§ 444) causes the shock as it shoots through the fingers.
(C) If you have electric bells or telegraph sounders use them for this experiment.
473. Induction Coils are instruments for producing induced currents of high E. M. F. The apparatus shown [200] in Fig. 141 forms a simple induction coil. ”