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That is, by dividing the resistance of the circuit in ohms, by the electromotive force of the current you will get the amperes flowing in the circuit. Finally if you know what the resistance of the circuit is in ohms and the current is in amperes then you can find what the electromotive force is in volts since: Ohms x Amperes = Volts, or R x I = E
In alternate current machines the electromotive force keeps constant, as the field- magnets are excited by a separate machine, giving a continuous current. We have already seen that the action of the dynamo is reversible, and that just as a wire moved across a magnetic field supplies an electric current, so a wire at rest, but conducting a current across a magnetic field, will move.
The intensity is not proportional to the electromotive force, and it increases at first as the electromotive force augments; but it approaches asymptotically to a maximum value which corresponds to the number of ions liberated, and can therefore serve as a measure of the power of the excitement. It is this current which is termed the current of saturation.
Rusty lead, so to speak, so connected with bright lead, has a high electromotive force. Oxygen makes lead rusty, and hydrogen makes it bright. Oxygen and hydrogen are the two gases cast off when water is subjected to a current.
It is commonly reserved for the arc lamp, which has a resistance so low that a moderate electromotive force can overcome the added resistance of the lamps, but, of course, if the circuit breaks at any point all the lamps go out. The parallel system is illustrated in figure 67, where the lamps are connected between two main conductors cross-wise, like the steps of a ladder.
It always flows in the same direction if the joint is not overheated, or, in other words, raised above a certain temperature. The electromotive force and current of a thermo-electric couple is very much smaller than that given by an ordinary voltaic cell. We can, however, multiply the effect by connecting a number of pairs together, and so forming a pile or battery.
That is, if you divide the current in amperes by the electromotive force in volts the quotient will give you the resistance in ohms. Or if you know what the electromotive force of the current is in volts and the resistance of the circuit is in ohms then you can find what the current flowing in the circuit is in amperes, thus: Volts E = Amperes, or = I Ohms R
Such resistance represents a length of eighteen miles of ordinary telegraph wire. After this, 700 ohms were overcome with 3.4 volts. This result was obtained by direct transmission, and without an induction coil, and it is probable that it might be much exceeded without sensibly increasing the electromotive force of the current. Le Genie Civil.
Just as water flowing through a pipe has quantity and pressure back of it and the pipe offers friction to it which tends to hold back the water, so, likewise, does electricity flowing in a circuit have: quantity, or current strength, or just current, as it is called for short, or amperage, and pressure, or potential difference, or electromotive force, or voltage, as it is variously called, and the wire, or circuit, in which the current is flowing has resistance which tends to hold back the current.
He deduces this from the electromotive force of a single battery cell which becomes thus connected with the values of the osmotic pressures, or, if you will, thanks to the relation discovered by Van t' Hoff, with the concentrations.
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