Electric charge

“ This result shews that under the action of any external electric forces on a homogeneous medium, the interior of which is originally charged in any manner with electricity, the internal charges will die away at a rate which does not depend on the external forces, so that at length there will be no charge of electricity within the medium, after which no external forces can either produce or maintain a charge in any internal portion of the medium, provided the relation between electromotive force, electric polarization and conduction remains the same. ”

“ 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. ”

“ The production of a state in which the volume density of the electrons carrying the current is as large as possible compared with the density of gas molecules in which there exists therefore a tendency for the formation of the maximum possible space charge in the path of the current.' To one skilled in the art, this could only mean that increased effectiveness of an electrical discharge device, to which a suitable current is applied, could be obtained by raising the vacuum in the manner which the writer had described. ”

“ The principle of induction is of the utmost generality in electric action. It constitutes charge in every ordinary case, and probably in every case; it appears to be the cause of all excitement, and to precede every current. The degree to which the particles are affected in this their forced state, before discharge of one kind or another supervenes, appears to constitute what we call intensity.
1300. When a Leyden jar is charged, the particles of the glass are forced into this polarized and constrained condition by the electricity of the charging apparatus. ”

“ It is this energy which, by the action of the machine, is converted into the potential energy represented by the electric field surrounding the two electrodes. To increase the charge it is customary to connect the electrodes with the knobs of two Ley den jars, since by the use of a condenser the quantity of electricity, which can be accumulated with a given difference of potential, is greatly augmented. That energy is used in producing electrification is distinctly felt when working the machine by hand. ”

“ So the potential distribution in the space due to the electric point-charge +q as A together with −q at B is the same as that due to +q at A and the negative induced charge erected on the infinite plane (earthed) metal sheet placed half-way between A and B.
The same reasoning can be applied to determine the electrical image of a point-charge of positive electricity in a spherical surface, and therefore the distribution of induced electricity over a metal sphere connected to earth produced by a point-charge near it. ”

“ If we wish it to go on further we must increase the source from which the negative charge of the cylinder is derived, that is, we must charge the sphere more strongly. How are we to increase this positive charge? The most obvious thing is to increase it also by mechanical means, much in the same way as we increase the charge on the third conductor, and this is the principle on which the modern electric machines, the so-called "influence machines," work. ”

“ Those circumstances which tend to facilitate the charge of the air by the excited conductor, and also those which tend to keep the tension at the same degree notwithstanding the discharge, assist in producing the glow; whereas those which tend to resist the charge of the air or other dielectric, and those which favour the accumulation of electric force prior to discharge, which, sinking by that act, has to be exalted before the tension can again acquire the requisite degree, favour intermitting discharge, and, therefore, the production of brush or spark. ”

“ In handling the lamp while making connections with the battery wires, care must be taken that the lamp wires are not broken off close to the glass by too much twisting. Should this happen, the lamp would be rendered useless, because then we could not get a connection with the carbon filament.
All the connections having been made, everything is ready to charge the battery. Charging means to fill the cells with the proper chemical solutions which, in their action upon the zinc and carbons, produce the electric current. ”

“ The discharge by a brush is not to all the particles of air that are near the electrified conductor from which the brush issues; only those parts where the ramifications pass are electrified: the air in the central dark parts between them receives no charge, and, in fact, at the time of discharge, has its electric and inductive tension considerably lowered. For consider fig. ”

“ The connexion between this view of gravity and that of the electrical constitution of matter is evidently very close, for if gravity arose in this way the weight of a body would only depend upon the number of units of electricity in the body. On the view that the constitution of matter is electrical, the fundamental units which build up matter are the units of electric charge, and as the magnitude of these charges does not change, whatever chemical or physical vicissitudes matter, the weight of matter ought not to be affected by such changes. ”

“ The great law which regulates these transactions is this: that the sum of the internal and the external heats is a constant quantity; so that when the platinum wire was ignited we had less heat developed in the battery than before. The zinc in the battery is burned as fuel upon a hearth; the heat, however, being developed either upon the hearth itself or at any distance from it.
“As a primary source of electricity here is the combustion of a metal, the voltaic battery is not an economical source of power for producing electric light. ”

“ It is greater, for instance, in dense air than in rare air, and greater in glass than in air, but in every case, if the electromotive force be made great enough, the dielectric gives way and its insulating power is destroyed, so that a current of electricity takes place through it. It is for this reason that distributions of electricity for which the electric resultant force becomes anywhere infinite cannot exist in nature. ”

“ Let us say that instead of separating these two mains by air we separated them by the human body—that a man took hold of the bare wires, one in each hand. The resistance of the human body varies from 5,000 to 10,000 ohms. In that case C (amperes) equals 110/5,000, or 110/10,000—about 1/50th, or 1/100th of an ampere. This illustrates why an electric current of 110 volts pressure is not fatal to human beings, under ordinary circumstances. ”

“ In this way the electrons at the far end of the wire commence to move at practically the same moment as those near the battery.
It has been a source of amusement to me to see people perfectly mystified by the fact that they can get no electric current unless they have a complete circuit. What else could they expect? How could man march if he had no road to march on? You see, the reason for our march is that we wish to escape from the overcrowding on the zinc, and we are forced towards the copper. ”

“ It will be observed that the segments of both discs, whilst passing each other on the horizontal diameter, are charged with electricity of the same sign, namely, positive on the left and negative on the right.
If we now inquire as to the true cause of electrification, we find that apart from the quite insignificant initial charge on A and B, it is simply the mechanical energy required to produce rotation against the opposing force of electrostatic attraction between the outer and inner segments. A has a positive, and a has a negative charge. ”

“ The current required to run a street car is about thirty amperes, and an electromotive force of about 180 volts. If cars are run in connection with an incandescent light station, we can arrange our apparatus so that we can use an E.M.F. say of 110 volts, and then we can put in a smaller number of cells with a larger capacity that will give a corresponding horse power. We can charge such larger cells with 50 or 60 amperes instead of thirty. ”

“ As it is a law of every electric circuit that the rate of transformation of electric energy to heat or work in each of its several parts is directly proportional to the drop of voltage therein, it follows that a drop of 500 or 1,000 or 2,000 volts in the conductors of a 10,000-volt transmission line at full load would correspond to a power loss of five to ten or twenty per cent respectively. ”

“ 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. ”

“ The electric current has likewise the property of heating a wire through which it passes. To prove this, let us connect the two poles of a battery by means of a fine platinum wire, when it will be found that the wire will, in a few seconds, become heated to redness. In point of fact, the current will heat a thick wire, but not so much as a thin one, for we may suppose it to rush with great violence through the limited section of the thin wire, producing in its passage great heat. ”

“ After the invention of the voltaic battery, early in the last century, experiments were made which determined that heat could be produced by the passage of the electric current through wires of platinum and other metals, and through pieces of carbon, as noted already, and it was, of course, also observed that if sufficient current were passed through these conductors they could be brought from the lower stage of redness up to the brilliant white heat of incandescence. ”

“ It is found that when the electromotive force begins to act, the current, as indicated by the galvanometer, is by no means constant. The first effect is of course a transient current of considerable intensity, the total quantity of electricity being that required to charge the surfaces of the insulator with the superficial distribution of electricity corresponding to the electromotive force. ”

“ In every point of the space surrounding such a conductor, there acts a force pushing positive electricity one way and negative electricity the opposite way. If the charged body is positively electrified, the potential will be positive all around it, but higher close to the body and lower the farther we recede from it. We must conceive a charge as a something which is adhering to a conducting surface; where there is no conductor there can be no charge, though there may be potential. ”

“ As the carrier of these charges is metallic, that is to say, offers no resistance to the free displacement or flow of electricity, there is nothing to hinder the movement, and consequently the charge will all accumulate on the outside surface. ”

“ Where currents of any magnitude are required, we must use other methods of producing electricity. These will be discussed subsequently, but for the present it is important to note that, apart from a question of degree, the frictional machine is an apparatus whereby electric currents may be generated.
How does the matter stand with regard to electrification by contact between solid bodies? Can we thereby also produce an electric current? We have seen that two metals in contact electrify each other. Using copper and zinc, the former becomes negatively and the latter positively electrified ”

“ All that I have said about the voltaic arc, the incandescence resulting from resistance to the current's flow, and so forth, in relation to electricity generated by galvanic batteries, applies to electricity generated by induction coils, or by magneto-electric and by dynamo-electric machines. Only it is to be noticed that in some of these machines the currents alternate in direction with each revolution of the swiftly turning coil, in others the currents are always in the same direction, and in yet others the currents may be made to alternate or not, as may be most convenient. ”

“ A wooden sphere covered with the thinnest layer of gold-beater's skin will at the same potential hold exactly the same quantity of electricity as if it were made of solid brass or lead or any other metal. Electricity at rest resides entirely on the outside of a metal conductor. We might reduce the thickness of a shell to any degree, and still the charge is not altered. ”

“ The best conductors offer some resistance to the passage of the current and the best insulators conduct to some extent. If we make a comparison of electric conductors we find that the metals that conduct heat best also conduct electricity best. This, it seems to me, is a confirmation of the atomic theory of electricity so far as it means anything. If a good conductor, as silver, is subjected to intense cold by putting it into liquid air, its conductivity is greatly increased. It is well known that [Pg 48] heating a conductor ordinarily diminishes its power to conduct electricity. ”

“ This true electrification must be distinguished from the apparent electrification , which is the electrification as deduced from the electrical forces in the neighbourhood of the surface, using the ordinary characteristic equation
If a solid dielectric of any form is a perfect insulator, and if its surface receives no charge, then the true electrification remains zero, whatever be the electrical forces acting on it. ”