Solenoid

“ If a solenoid forms a closed curve the potential due to it is zero at every point, so that such a solenoid can exert no magnetic action, nor can its magnetization be discovered without breaking it at some point and separating the ends. ”

“ For a thin endless solenoid the axial magnetic force is therefore 4π times the current-turns per unit of length. This holds good also for a long straight solenoid provided its length is large compared with its diameter. It can be shown that if insulated wire is wound round a sphere, the turns being all parallel to lines of latitude, the magnetic force in the interior is constant and the lines of force therefore parallel. ”

“ When the circuit of the lamp is completed with the electric generator the carbons are drawn apart by the action of the solenoid on the plunger, and the distance to which they are separated is determined by the difference of attractive force exercised upon the armature by the solenoid and the magnet ”

“ The same would be the case if the magnetization of the filament varied inversely as the area of its cross-section a in different parts. Such a filament is called a simple magnetic solenoid, and the product aI is called the strength of the solenoid. A magnet which consists entirely of such solenoids, having their ends either upon the surface or closed upon themselves, is called a solenoidal magnet, and the magnetism is said to be distributed solenoidally; there is no free magnetism in its interior. ”

“ A solenoid wire is a single straight wire, connected at each end with and wound closely around by another insulated wire, this forming a complete system, the electric currents returning into themselves. Electricians claim that the solenoid effectually overcomes all induction, and this afternoon experiments were made for the purpose of proving that assertion. In the telephones, connected by the ordinary wires, a constant burr and click could be heard, that sound being the induction from the wires on the poles on Market Street, sixty feet overhead. ”

“ These solenoids, by means of a suitable mechanism, act in opposition, the current solenoid separating the carbons, and the potential difference solenoid bringing them closer together. The actions balance one another when the arc is of the correct length.
Such an arrangement also serves to strike the arc when the supply is switched on. In order to prevent the arc from wandering round the carbons, the positive carbon is cored, and sometimes the negative carbon also. The core consists of purer softer carbon of lower resistance, and the arc remains centrally placed. ”

“ The solenoid winding is in series with the dynamo circuit and when the load is normal, the spring pull is just equal to the magnet pull, and the resistance of A and B are equal. When external load varies, a small but proportional variation in the pull of P charges the relative resistances of the piles and the booster field is energized to produce a voltage to cause battery charge or discharge. ”

“ The middle solenoid is hung from the end of a balance beam, and its motion is retarded by a counterweight, which admits of regulating the meter to give standard measure as a clock gives standard time. The motion of the beam is caused to incline the integrating wheel, and the rotation of the cylinder gives the energy expended in foot-pounds by means of an indicator or diagram, as the case may be. ”

“ The solenoid used to produce a magnetic field across the glass cylinder, which is filled with carbon bisulphide, is in circuit with a dynamo, resistances, and the screens on the gun range. It is a well-known phenomenon in physics that when, with the above-mentioned combination of polarizing Nicol prism and analyser, the light is shut off by rotating the analyser, it is instantly restored when the carbon bisulphide is placed in a magnetic field. This phenomenon is utilized in this instrument. The projectile, by cutting the wire screens, causes the magnetic field to cease and light to pass. ”

“ In the upper figure, the air space or “air core” surrounded by the solenoid offers considerable resistance to the passage of magnetic lines, allowing only a small number to pass through. If a piece of iron be introduced, as in the lower figure, the number of lines will be greatly increased. The number of lines B passing through a unit cross section of the iron core divided by the number of lines H, passing through a unit cross section of the air core is called the permeability and designated by the Greek letter μ.
In other words, it is the ratio of flux density to magnetizing force. ”

“ Let the resistance of unit of length of a wire, such that windings occupy unit of length of the solenoid, be .
The resistance of the whole solenoid is
.
(32)
The condition that, with a given value of , may be a maximum is , where is some constant.
This gives proportional to , or the diameter of the wire of the exterior coil must be proportional to the square root of the radius.
In order that, for a given value of R, g may be a maximum
. ”

“ When such a condition is fulfilled, it is found that if we try to remove the iron cylinder from the equilibrium that it is in, we must apply a pressure that increases with the amount of separation, just exactly as if it were suspended from a spring. It results from this fact that if we displace the brushes a distance equal to the thickness of one plate of the collector, the active solenoid will undergo the same displacement, and its longitudinal center will move away from that of the iron cylinder, and that the attraction exerted upon the latter will increase. ”

“ If a magnet can be divided into solenoids, all of which either form closed curves or have their extremities in the outer surface of the magnet, the magnetization is said to be solenoidal, and, since the action of the magnet depends entirely upon that of the ends of the solenoids, the distribution of imaginary magnetic matter will be entirely superficial. ”

“ The action of a closed solenoid is zero.
(3) The action of a circuit C on another voltaic circuit C' depends only on the "magnetic field" developed by the circuit C. At each point in space we can, in fact, define in magnitude and direction a certain force called "magnetic force," which enjoys the following properties:—
(a) The force exercised by C on a magnetic pole is applied to that pole, and is equal to the magnetic force multiplied by the magnetic mass of the pole. ”

“ Lamps through whose
regulating mechanism the whole current passes. These are only adapted to
work singly; if several are placed in series on the same circuit, the
action of one regulator interferes with that of the next one.
(b) Multiple light regulators or polyphotes. In these the regulating
mechanism and the carbons with their arc are in parallel; the regulating
device may be a single magnet or solenoid constituting a derived or
shunt-circuit lamp, or it may include two magnets working differentially
against or in opposition to each other constituting a differential lamp. ”

“ If the cylinder, instead of being a magnetized body, is uniformly lapped with wire, so that there are windings of wire in unit of length, and if a current, , is made to flow through this wire, the magnetic potential outside the solenoid is as before,
. ”

“ Fig. 754.--Wiring diagram of the standard form of Monitor controller. A set of solenoids are connected in series and so interoperating as to cut resistance out of the armature circuit of the motor as the apparatus it is driving comes up to speed. The controller is designed to be used on all classes of work. In its simplest form, a single copper and graphite contact, is controlled by two magnets, so proportioned as to cut out the entire starting resistance when the armature current falls to a predetermined value. ”

“ If we suppose any surface divided into elementary portions such that the surface-integral of each element is unity, and if solenoids are drawn through the field of force having these elements for their bases, then the surface-integral for any other surface will be re presented by the number of solenoids which it cuts. ”

“ A current in a small circular conductor exerts a magnetic force in its centre perpendicular to its plane and is in all respects equivalent to a magnetic shell or a thin circular disk of steel so magnetized that one face is a north pole and the other a south pole, the product of the area of the circuit and the current flowing in it determining the magnetic moment of the element. (4) A closely wound spiral current is equivalent as regards external magnetic force to a polar magnet, such a circuit being called a finite solenoid. ”

“ In some regulators the work of moving the regulator is
executed mechanically, but under electrical control; in others the
entire work is done by the current.
A typical regulator or governor (Golden's) of the first class comprises
two driven friction wheels between which is a driving friction wheel,
which can engage with one driven wheel only at once. It is brought into
engagement with one or the other by a solenoid and plunger.
455 STANDARD ELECTRICAL DICTIONARY.
As it touches one wheel it turns it in one direction. ”

“ Mr. Tedder wanted to give his class a good show. So, with more feeling for dramatic effect than for scientific good sense, he'd wound the three solenoids with heavy insulated silver wire rather than with the light copper wire Ziegler had reported using. ”

“ Let V be any continuous function of and let be functions of subject to the general solenoidal condition
where these functions are continuous, and to the superficial solenoidal condition
at any surface at which these functions become discontinuous, being the direction-cosines of the normal to the surface, and and the values of the functions on opposite sides of the surface, then the triple integral
vanishes when the integration is extended over a space bounded by surfaces at which either is constant, or
being the direction-cosines of the surface. ”

“ When the magnet is solenoidal the expression under the integral sign in the second term is zero for every point within the magnet, so that the triple integral is zero, and the scalar potential at any point, whether outside or inside the magnet, is given by the surface-integral in the first term. ”

“ Armature Reaction in Motors.—In the operation of a motor the reaction between the armature and field magnets distorts the field in a similar manner as in the operation of a dynamo. A current supplied from an outside source magnetizes the armature of a motor and transforms it into an 364 electromagnet, whose poles would lie nearly at right angles to the line joining the pole pieces, were it not for the fact that negative lead must be given to the brushes. ”

“ An armature for a motor or dynamo, the ends of all of whose coils are
united, so as to be in one closed circuit all the way around.
Fig. 23. CLOSED COIL GRAMME RING ARMATURE.
Armature Coil, or Coils.
The insulated wire wound around the core of the armature of an electric
current generator or motor.
Armature Core.
The central mass of iron on which the insulated wire, to be rotated in
the field of an electric current generator or motor, is wound. (See
Dynamo-electric Machine and Motor, Electric.) ”

“ The passage of the alternating current through the armature winding produces a magnetic field that rotates about the armature core, and induces in the pole pieces eddy currents, which, reacting on the armature, exert a sufficient torque to start the converter from rest and cause it to speed up to synchronism. ”

“ The motion of one has, therefore, an analogy in the motion of the other. In an electrical circuit having a coil and a condenser the moving electricity has a definite inertia and a definite electrical stiffness; hence it will have a definite pitch or frequency for its vibratory motion, just like a tuning-fork; it will act as a resonator. It is obvious, therefore, that an electrical resonator, the pitch of which can be adjusted by adjusting its coil or its condenser or both, is a perfect parallel to the acoustical resonator. ”

“ Commutator.—That part of a dynamo-electric machine to which all of the armature wires are connected and in which the alternating-electromotive force, actually generated in the armature winding, is made to appear as a direct-electromotive force in the external circuit. ”

“ Turn slowly and you notice that the alternations of the current are numbered by the strokes on the bells. The hammer swings to and fro just as the needle of the ammeter did. Each bell therefore receives one stroke of the hammer for each revolution of the armature. Now try to turn the crank steadily at the rate of one revolution per second. The armature is making six revolutions, or cycles, per second and you now have not only an alternating current dynamo but a six-cycle alternating current dynamo. [22] The lighting circuit used in our apartment is a sixty-cycle alternating current. ”

“ As the top of the core leaves or breaks the contact flow of current, the bottom of the core comes in contact range, leaving an open space which breaks the current and changes the direction of flowage as shown in Fig. 58A and 58B. This current is of a low tension nature, and will not jump the gap at the [103] spark plugs when the engine is running slow. The secondary winding, shown in Fig. 58, is made up of many more windings of a finer wire. The low tension or primary current is led through the armature shaft to a contact breaker at the rear of the magneto. ”