Ohm

“ He was one of the first in this country to appreciate the importance of Ohm's simple law of the relation between electromotive force, resistance of conductors, and resulting current—the law which is today the foundation of all electrical engineering. ”

“ If a current be passed through two resistances in series by means of an applied electromotive force, the electric potential falls from one end of the resistances to the other, and, if we apply Ohm’s law to each resistance in succession, we see that, since for each of them E = CR, and C the current is the same through both, E the electromotive force or fall of potential between the ends of each resistance must be proportional to the resistance between them. ”

“ Henry:—From Joseph Henry, of the Smithsonian Institution, Washington, D. C. The practical unit for measuring the induction in a circuit when the electro-motive force induced is one international volt, while the inducing current varies at the rate of one ampere per second.
Joule:—The C. G. S. unit of practical energy, being equivalent to the work done in keeping up for one second a current of one ampere against a resistance of one ohm. ”

“ It is the electrical resistance of a rod of copper of a certain length and thickness when at a certain temperature. The electric pressure or difference of potential which will send a certain amount of current, called an 'ampere,' through a conductor the resistance of which is an ohm, is one volt. ”

“ Here four storage cells in series have an E.M.F. of 8 volts and in accordance with Ohm's law produce a current of 2 amperes through a resistance in the circuit of 4 ohms. Now the work done or energy expended by the current in passing through the resistance between the points M and N depends upon three factors (1) the E.M.F. or potential difference; (2) the current intensity and (3) the time. The energy is measured by their product. That is, electrical energy = potential difference × current intensity × time. ”

“ Let be the electromotive force in a linear conductor from the electrode to the electrode . (See Art. 69.) Let be the strength of the electric current along the conductor, that is to say, let units of electricity pass across every section in the direction in unit of time, and let be the resistance of the conductor, then the expression of Ohm's Law is ”

“ Since, other things being equal, the rise in electromotive force due to resonance is directly proportional to the magnitude of the harmonics, and the chance of getting it increases rapidly with the presence of those of the higher orders, the desirability of using the closest possible approximation to a sinusoidal wave is self-evident. The greater the inductance and capacity of the system and the less its ohmic resistance, the greater the chance of getting serious resonance. ”

“ The resistance of the earth communication of the conductor, measured through the uninjured fragment, was sixty-five ohms—that is, some twelve or sixteen times greater than under any circumstances it ought to have been. ”

“ Fig. 1,319.—Graphical method of finding angle of lag when the ohmic drop and reactance drop are given. The angle of lag φ, is that angle included between the impressed pressure and the ohmic drop lines, that is, between AC and AB.
EXAMPLE.—An alternating current of 10 amperes having a frequency of 60, is impressed on a circuit containing a resistance of 5 ohms and an inductance of 15 milli-henrys. ”

“ When the alternations of the current are very rapid, the ohmic resistance ceases to play a dominant part, and the ordinary equations connecting electromotive force, induction, and current are equivalent to the conditions that the currents shall be so distributed as to make the electrokinetic or magnetic energy a minimum. Consider now the case of a single straight wire of circular cross-section. ”

“ The ratio of any impressed electro-motive force to the current which it
produces in a conductor. For steady currents it is only the resistance.
For variable currents it may include besides resistance inductance and
permittance. It is the sum of all factors opposing a current, both ohmic
and spurious resistances. It is often determined and expressed as ohms. ”

“ If an electrical engineer finds a resistance of a hundred ohms, he will rightly pronounce the earth contact to be very bad indeed. But why should the lightning flash leave a conductor with a resistance of a hundred ohms in order to follow a line of non-conductors where it encounters a resistance of many thousand ohms? ”

“ If such an arc lamp is connected to a source of electric supply having an electromotive force preferably of 100 volts, and if some resistance is included in the circuit, say about 5 ohms, a steady and continuous arc is formed when the carbons are brought together and then slightly separated. ”

“ The ampères used multiplied by the number of volts give the total power consumed in watts, and 1000 watts used for one hour represent 1 unit as charged for on our dreaded lighting bills. The current available from a public supply may be said to be unlimited so far as our purpose is concerned, and the amount actually used depends only on the total electrical resistance of our circuit, and this is measured in ohms, the three factors, viz. ”

“ I Works.--When the electric waves from a distant sending station impinge on the wire of a receiving aerial their energy is changed into electric oscillations that are of exactly the same frequency (assuming the receptor is tuned to the transmitter) but whose current strength (amperage) and potential (voltage) are very small. These electric waves surge through the closed circuit but when they reach the crystal detector the contact of the metal point on the crystal permits more current to flow through it in one direction than it will allow to pass in the other direction. ”

“ A similar effect is produced when reversed undulatory currents are employed as shown in fig. 14, where the current is produced by the vibration of permanent magnets M M ́ in front of electro-magnets (e e ́) , united upon a circuit without a voltaic battery. It will be understood from figs. 13 and 14 that the effect of transmitting musical signals of different pitches simultaneously along a single wire is not to obliterate the vibratory character of the current as in the case of intermittent and pulsatory currents, but to change the shapes of the electrical undulations. ”

“ The minute currents here employed are far surpassed as regards delicacy and frequency by those revealed to us by that marvel of the present day, the telephone. The electric currents caused by the vibrations of a diaphragm acted upon by the human voice naturally vary in frequency and intensity according to the number and degree of those vibrations, and each motor-current, in exciting the electro-magnet forming part of the receiving instrument, deflects the iron diaphragm occupying the position of an armature to a greater or smaller extent according to its strength. ”

“ He regarded the outer layers as different from the mass of the metal and having a much greater specific resistance. He supposed that when two pieces of metal are pressed together the molecules diffuse across the surface, modifying the surface layers and increasing their conductivity.
§ 8. Generators of Electric Waves.—Bose (Phil. Mag. 43, p. 55) designed an instrument which generates electric waves with a length of not more than a centimetre or so, and therefore allows their properties to be demonstrated with apparatus of moderate dimensions. ”

“ OSCILLATIONS, ELECTRIC.--A current of high frequency that surges through an open or a closed circuit. (1) Electric oscillations may be set up by a spark gap, electric arc or a vacuum tube, when they have not only a high frequency but a high potential, or voltage. (2) When electric waves impinge on an aerial wire they are transformed into electric oscillations of a frequency equal to those which emitted the waves, but since a very small amount of energy is received their potential or voltage is likewise very small. ”

“ When notes were sung or words spoken before one drumhead, the vibrations of the goldbeaters’ skin carried the small piece of clockspring267 vibratingly towards and from the electro-magnet, without producing actual contact. Now, the current which was passing along the coil round the electro-magnet changed in strength with each change of position of this small piece of metal. The more rapid the vibrations, and the greater their amplitude, the more rapid and the more intense were the changes in the power of the electric current. ”

“ In effecting a complete severance of the conductor for a short distance, after the current has been established, a very great local resistance is occasioned, giving rise to the electric arc, the highest development of heat ever attained. Vibration is another form of lost energy in mechanism, but who would call it a loss if it proceeded from the violin of a Joachim or a Norman-Neruda?
Electricity is the form of energy best suited for transmitting an effect from one place to another ”

“ To sum up, we may then say that whenever rapid electrical oscillations are created in open circuit, such as the two rods above described, the arrangement constitutes a device for creating an impulse or effect in the surrounding space called an electric wave in the æther or electro-magnetic medium; just as an organ-pipe or piano-string or other musical instrument constitutes a device for creating waves in the air by means of mechanical oscillations. ”

“ I touch the lamps before me and feel them warm because the heat of the incandescent material which they contain has thrown the molecules of the covering glass into vibration, and that vibration imparts a vibration to my hand that gives the sensation of heat; and if I were to put a poker in the fire—which, no doubt, all of you have done—it would be found in a very short time that the heat of the fire had been transferred through the poker to your hand. Electric currents are a form of energy which is driven through matter. Electricity is transferred, principally, through metals ”

“ 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. ”

“ A blunt body must be brought within an inch, and draw a spark, to produce the same effect. To prove that the electrical fire is drawn off by the point, if you take the blade of the bodkin out of the wooden handle, and fix it in a stick of sealing wax, and then present it at the distance aforesaid, or if you bring it very near, no such effect follows ”

“ A building or a ship - just as I have indicated - may develop "vibrations," even as certain materials in combination under the proper conditions will certainly develop an electric current.
'To say more in a talk of this scope is useless. I am more inclined to remind you of the glass which will vibrate to a certain note struck upon a piano and to silence all your worrying questions with that simple little unanswered one: What is electricity? When we've got that clear it will be time to take the next step in a more dogmatic fashion. ”

“ The fourth kinds of waves, which go out from the spark gap of our coil, are also waves in the ether. They are still longer than heat or light. We have ears for sound, eyes for light, and temperature sensation for heat, but as yet we have not evolved a delicate sense organ for detecting electric waves. At least few of us claim to have such a sense. I will, however, undertake to make you feel electricity. I then adjusted the coil so that each boy might take a mild electric shock from it by touching the two knobs. That is by placing himself in the spark gap. ”

“ The volt-coulomb is very seldom used, and the unit of Electric Activity
or Power (see Power, Electric) , the volt-ampere, is universally used.
This unit is sometimes called the Watt, q. v., and it indicates the rate
of expenditure or of production of electric energy.
The storing up in a static accumulator or condenser of a given charge of
electricity, available for use with a given change of potential
represents potential electric energy.
The passing of a given quantity through a conductor with a given fall of
potential represents kinetic electric energy. ”

“ Here we have evidence of a force causing an electric current in spite of resistance; electrifying the extremities of a body in opposite ways, a condition which is sustained only by the action of the electromotive force, and which, as soon as that force is removed, tends, with an equal and opposite force, to produce a counter current through the body and to restore the original electrical state of the body ”

“ This I have proved by the discovery that when two or more electrical conducting bodies are placed in contact under very slight constant pressure, resting on any body whatever, they will of themselves transform a constant electrical current into an undulatory current, representing in its exact form the vibrations of the matter on which it reposes; it requires no complicated arrangement and no special material, and to most experimenters the three simple iron nails that I have described form the best and most sensitive microphone. ”

“ In one the body of a person was subjected to the rapidly-alternating pressure of an electrical oscillator of two and a half million volts; in the other a small incandescent lamp was lighted by means of a resonant circuit grounded on one end, all the energy being drawn through the earth electrified from a distant transmitter. ”