Electric conductor

“ If a piece of metal be presented to an over-charged prime conductor, the fluid passes with violence from the one to the other; an electric spark, having the appearance of fire, is seen flashing between them, and a snapping noise, like the cracking of a whip, is heard. If this piece of metal be insulated, the prime conductor will be only partially discharged, that is, the redundant electricity will be divided between it and the piece of metal, nearly in proportion to their surfaces. ”

“ Now the very definition of a conductor is a body over the surface of which electricity can distribute itself without hindrance, that is to say, only under the influence of the potential force that pushes it. The region of space surrounding the charged in which the potential has a sensible value is called the "electric field." A unit charge brought into any point of this field will experience a force acting in a certain direction; in the case of the field being due to the presence of a charged sphere the force acts either radially outward from or radially inward to the centre of the sphere. ”

“ If the shaft which supports the loop is rapidly revolved; a current of electricity will be set up in the wire loop by bridging over the space at the ends of the wire between the metal plates with a piece of metal or another loop of copper wire; copper always being used to conduct electricity where it can be, for the reason that it is the best practical conductor of electricity. ”

“ The greater diameter of aluminum over equivalent copper conductors has advantages in transmission with alternating current at very high voltages. At high voltages, say of 40,000 or more, the constant silent loss of energy from one conductor to another of the same circuit through the air tends to become large and even prohibitive in amount. ”

“ We find that electromotive force acts differently on various substances when they are subjected to its operation. In some substances electromotive force produces a continuous electric current, and in these cases the material is called a conductor. In other cases electromotive force creates what is called electric strain, or electric displacement, and these substances are generally called non-conductors. ”

“ By this we mean that to get the current through the wire the force which is pushing the electricity from one end to the other is much smaller with silver than with lead; silver offers less "resistance" to the flow of electricity than lead. Thus each conductor has a certain physical property called its electric resistance, and this depends on the length and section of the conductor, on its temperature and on its material. In order to compare different materials as regards resistance, we must eliminate those elements which may vary from case to case and reduce all to the same standard. ”

“ On most, if not all, transmission lines the guard wire or wires, if used at all, are placed either above or on a level with the highest power conductors. With one conductor of a three-phase circuit mounted on a pin set in the top of a pole, and the two remaining conductors on a two-pin cross-arm beneath, in the method most frequently adopted for transmission lines of very high voltage, it is obviously impracticable to put guard wires either above or on a level with the power circuits. ”

“ If the electrified tray is touched with the sealing-wax or ebonite rod, it will not be discharged, but if touched with a metal wire, the hand, or a damp thread, it is discharged at once. This shows that some bodies are conductors and others non-conductors or insulators of electricity, and that bodies can be electrified by friction and impart their electric charge to other bodies. A charged conductor supported on a non-conductor retains its charge. ”

“ In the arc-lamp the electric circuit is broken at the point where light is required. In glow or incandescent lamps the current is only hindered by the interposition of a bad conductor of electricity, which must also be incombustible. Just as a current of water flows in less volume as the bore of a pipe is reduced, and requires that greater pressure shall be exerted to force a constant amount through the pipe, so is an electric current choked by its conductor being reduced in size or altered in nature. ”

“ However, with incomparably higher frequencies, which we may yet find means to produce efficiently, and provided that electric impulses of such high frequencies could be transmitted through a conductor, the electrical characteristics of the brush discharge would completely vanish—no spark would pass, no shock would be felt—yet we would still have to deal with an electric phenomenon, but in the broad, modern interpretation of the word. ”

“ Inductance increases with the frequency of the current in a conductor, and in each of the three systems just considered the frequency is sixty cycles per second.
The use of one circuit of larger wire instead of two circuits of smaller wire has the obvious advantage of greater mechanical strength in each conductor, saves the cost of one pole line and of the erection of the second circuit. With voltages above 40,000 to 50,000 on long transmission lines there is a large loss of energy by leakage directly through the air from wire to wire. ”

“ Suppose, for instance, that a piece of fine wire be fixed between the pole wires of the battery; it will be heated “white hot.” Or if two carbon points be approached in a glass of water, as in the illustration (fig. 227) , they will emit a brilliant light in the fluid from the voltaic arc which has given us the electric light. The current is the passage of electricity along the wire, and continues [Pg 224] until the working power or “potential” of one conductor is equal to that of the other. When they become equal of course the action ceases, as there is equilibrium. ”

“ In like manner the hand, if brought near enough to the conductor, receives or gives an electric discharge; now we have no evidence that a charged conductor can be suddenly discharged unless by the approach of a body oppositely electrified In the case, therefore, of the electric machine, it appears that the accumulation of electricity in an insulated conductor is always accompanied by the excitement of the contrary electricity in the surrounding atmosphere, and in every conductor placed near the former conductor. It does not seem possible, in this case, to produce one electricity by itself. ”

“ We do not know precisely what electricity is, and by implication we do not know precisely what an electric current is, but we have all requisite knowledge about it for practical purposes. An electric current is a something which occurs in a conductor, i.e. a piece of metal when it connects two points between which there is electric pressure. The current may be only momentary, as in the case of Franklin's kite with a wire attached which was sent up into a thundercloud, or when a so-called Leyden jar is discharged ”

“ A disused and abandoned electric conductor, such as a telegraph
wire.
(c) A wire in use, but through which, at the time of speaking, no
current is passing.
Death, Electrical.
Death resulting from electricity discharged through the animal system.
The exact conditions requisite for fatal results have not been
determined. High electro-motive force is absolutely essential; a
changing current, pulsatory or alternating, is most fatal, possibly
because of the high electro-motive force of a portion of each period. ”

“ But if we connect these wires to the coils of the induction apparatus and then take hold of the two ends of the secondary coil and break and close the primary circuit we should feel a painful shock at each break and close, although the actual amount of current flowing through the secondary wire is not as great as that which flows through the primary; but the voltage (or electromotive force) is higher, and thus is able to drive what current there is through a conductor of higher resistance, such as the human body. ”

“ Can we conduct from one place to another this peculiar state of things, this queer form of potential energy which we call electrification? It is clear, from the last experiments, that in order to do it we need something besides ebonite, which really acts like a closed stop-cock to the flow of electrification.
To keep electrification in one place we need an insulator; to get it from one place to another we need a conductor. Insulators are as important as conductors. ”

“ A stout wire will transfer a bigger quantity in unit time than a thin wire, or, as we may also say, it is able to carry a bigger current. When it is a question of electricity in motion the conductor must have body, whilst as we have seen, with electricity at rest only the surface counts, or, to speak more correctly, only the capacity counts. ”

“ All wires have a certain resistance per foot, according to the nature of the metal used and the size of the wire—that is to say, the finer the wire the greater number of ohms resistance it has to the foot.
Water and electricity flow under very similar conditions—that is to say, each of them must have a channel, or conductor, and each of them requires pressure to force it onward. Water, however, being a tangible substance, requires a hollow conductor; while electricity, being intangible, will flow through a solid conductor. ”

“ In discharging electrical jars, the electricity goes in the greatest quantity through the best conductors, and by the shortest passage. Thus if a chain and a wire be made to communicate at the same time with the outer coating of a jar, and be both presented to the knob of that jar, the greater part of the charge will pass by the wire, and very little by the chain, because the latter is a worse conductor than the former, on account of its discontinuation at every link. When the discharge is 29made by the chain only, sparks are seen at every link, which is a proof they are not in contact. ”

“ If the positive and negative conductors of a frictional machine are connected by a wire, the charges rush along this wire to equalise each other, leaving both conductors without charge. We may imagine a simultaneous movement of positive and negative electricity along this wire in opposite directions, or we may imagine only the positive charge flowing along the wire in the direction of the negative conductor and spreading itself over its surface, and thereby neutralising the negative charge previously accumulated on it. ”

“ So long as the two plates of metal are not otherwise connected there is no electricity in evidence, but when the two are joined by any metal conductor, as, for example, a piece of wire—thus, in common parlance, "completing the circuit"—a current of electricity flows about this circuit, passing from the first metal plate to the second, through the liquid and back from the second plate to the first through the piece of wire. ”

“ In many electrical instruments a wire grating is used to prevent certain parts of the apparatus from being electrified by induction. We know that if a conductor be entirely surrounded by a metallic vessel at the same potential with itself, no electricity can be induced on the surface of the conductor by any electrified body outside the vessel. ”

“ In order that we may fully comprehend the nature of an insulation, let us make clear a few facts concerning conductors in general. All materials conduct electricity to a certain extent; but some with much more freedom than others. Thus, silver, copper, gold, zinc, platinum, iron, steel, mercury, and other pure metals permit the passage of an electric current through them with but slight resistance, (although all offer a certain amount,) and are therefore termed conductors. ”

“ On turning the plate, a faint snapping sound is heard, and when the room is darkened, a spark is seen to be thrown out from the knob projecting from the prime conductors.
Many curious and interesting experiments may be performed by means of the machine, illustrating the general properties of electricity. For instance: a person standing on an insulated bench, that is, a bench with glass legs, or having the legs resting on glass, and having one hand on the conductor, can send sparks, with the other hand, to everything and everybody about. This illustrates communication of electricity by contact. ”

“ Every one knows that when by means of an ordinary electrical machine electricity has been generated in sufficient quantity and under suitable conditions to prevent its dispersion, a spark of intense brilliancy and greater or less length, according to the amount of electricity thus collected, can be obtained when some body, not similarly electrified, is brought near to what is called the conductor of the machine. ”

“ How quickly a spoon inserted into a hot cup of tea becomes uncomfortably hot, though the hand can be held very close to the liquid without feeling more than a gentle warmth. And we all have noticed that the very least air-gap in an electric circuit effectively breaks a current capable of traversing miles of wire. If the current is so intense that it insists on passing the gap, it leaps across with a report, making a spark that is at once intensely bright and hot. Metal wires are to electricity what speaking tubes are to sound; they are as it were electrical tubes through the air and ether. ”

“ If you were to use a piece of string instead of a copper wire to go from one pole of a battery to another or to spin between the poles of the magnet of the dynamo, you could get no flow of electricity to speak of. Electrons do not flow through string easily, but they flow through a copper wire very easily. Anything that carries, or conducts, electricity well is called a good conductor. Anything that carries it poorly is called a poor conductor. Anything that allows practically no electricity to pass through it is called an insulator. ”