Ampere

“ You can’t make an ampere out of a piece of platinum as you can a standard pound weight. An ampere is a stream of electrons at about the rate of six billion billion a second. No one could ever count anywhere near that many, and yet everybody who is concerned with electricity wants to be able to measure currents in amperes. ”

“ An ampere is the unit rate of flow of the current, and a coulomb is the unit quantity of electricity, that is, the ampere is the rate of current flow that will deposit .0003286 grammes of copper in one second and a coulomb is the quantity of electricity that passes a given point in one second when the current strength is one ampere. ”

“ In the matter of ampere turns, as another example, it is quite simple to assert that a ten ampere current carried once around a soft iron bar produces the same result as a one ampere current carried ten times around the bar, but how much more strongly is this fact stamped upon the memory when its truth is established by experiment? ”

“ Just to give you an idea of the quantity of current an ampere is we will say that a dry cell when fresh gives a current of about 20 amperes. To measure the current in amperes an instrument called an ammeter is used, as shown at A in Fig. 30, and this is always connected in series with the line, as shown at B.
Electromotive Force and the Volt.--When you have a pipe filled with water or a circuit charged with electricity and you want to make them flow you must use a pump in the first case and a battery or a dynamo in the second case. ”

“ Unit electromotive force (volt) through unit resistance (ohm) gives unit of current (ampère) . It is not the intention to treat the subject mathematically, but I will give you a simple formula for finding the amount of current if you know the resistance and the voltage. The electromotive force divided by the resistance gives the current. C = E / R or current (ampères) equals electromotive force (volts) divided by the resistance (ohms) .
But still further: One ampère of current having one volt pressure will develop one watt of power, which is equal to 1/746 of a horse-power. ”

“ Don’t try to remember this number but do remember that an ampere is a unit in which we measure currents just as a year is a unit in which we measure time. An ampere is a unit in which we measure streams of electrons just as “miles per hour” is a unit in which we measure the speed of trains or automobiles. ”

“ An ampere foot may be defined as the product of one ampere multiplied by one foot.
The unit ampere foot is used in figuring motor circuits or currents designed to carry a mixed load.
Fig. 820.—The center of distribution of a circuit coincides with the geometrical center of the group of lamps when the lamps are of uniform size and spaced equal distances apart. The center of distribution is here indicated by the dotted line A B.
The ampere feet of a main are found by multiplying the maximum load in amperes by the distance from the fuse block to the electrical center of the load. ”

“ We will now connect with our laboratory current a 32-candle-power lamp, an ammeter, and a wattmeter, all in series, Fig. 18, and in parallel with these a volt meter. This last instrument indicates the electric pressure. Its mechanism will be examined later. The volt meter indicates 110 volts and the ammeter shows that one ampere is passing. [41] The filament in the lamp resists the passage of the current. It gets quite hot and gives forth as much light as thirty-two candles. Its resistance is just such that 110 volts of pressure send one ampere through it. ”

“ The quantity of electricity passed by a current of one ampere in one
hour. It is used by electric power and lighting companies as the unit of
energy supplied by them, because they maintain a constant potential
difference in their leads, so that only the amperes and hours need
measuring or recording to give the energy, viz. : volt-ampere-hours.
The same unit is applied to batteries to indicate their potential
energy, because they also are assumed to be of constant voltage or
electro-motive force. ”

“ That an unvarying current which, when passed through a solution of nitrate of silver in water, in accordance with the specification attached to this report, deposits silver at the rate of 0.001118 of a gramme per second, may be taken as a current of 1 ampere.
(11) That an alternating current of 1 ampere shall mean a current such that the square root of the time-average of the square of its strength at each instant in amperes is unity. ”

“ Currents from the ten-thousandth of an ampere to ten thousand amperes, electrical pressures from a minute fraction of a volt to 100,000 volts, come within the range of his instruments, while the private consumer of electric energy is provided with a meter recording Board of Trade units. ”

“ Kelvin ampere balances are made in two types— (1) a variable weight type suitable for obtaining the ampere value of any current within their range; and (2) a fixed weight type intended to indicate when a current which can be varied at pleasure has a certain fixed value. An instrument of the latter type of considerable accuracy was designed by Lord Kelvin for the British Board of Trade Electrical Laboratory, and it is there used as the principal standard ampere balance. A fixed weight is placed on one coil and the current is varied gradually until the balance is just in equilibrium. ”

“ If we should increase the voltage tenfold more, say the 110-volt dynamo current (direct current) , and touch the bare conductors with our hands, the ammeter would indicate about .001 ampere. That is, although this current has about seventy times as much push, or voltage, as a dry cell, no more electricity passes through the fingers than did through the tongue in the preceding experiment with one cell. The fingers offer so much greater resistance. ”

“ Mere change of scale may not at first appear a very important matter, but it is surprising how much modification it entails in the instruments, and in the processes of measurement. For instance, the resistance-coils on which the electrician relies in dealing with currents whose maximum is a fraction of an ampere, fail altogether when it becomes a question of hundreds, not to say thousands, of amperes. ”

“ An ammeter or ampere meter is simply a commercial form of galvanometer so constructed that the deflection of the needle indicates directly the strength of current in amperes. A good ammeter should have a very low resistance so that very little of the energy of the current will be absorbed; the needle should be dead beat, and sufficiently sensitive to respond to minute variations of current. ”

“ 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. ”

“ 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. ”

“ The opposition which one’s self-induced conscience offers depends upon how rapidly one starts. It’s volts which make electrons move and so the conscience which opposes them will be measured in volts. Therefore we say that a coil has one henry of inductance when an electron stream 85which is increasing one ampere’s worth each second stirs up in the coil a conscientious objection of one volt. ”

“ This apparatus, if charged to saturation, gives 62 ampere hours as its total capacity, and, as in the Plante, this capacity constantly increases with use. The normal rule for the charge is 10 amperes per square meter, and for the discharge double this quantity. This apparatus has always given me on discharging 40 amperes at the E.M.F. of 1.85 volts during 60 or 65 minutes. The charge is effected in two hours up to 20 amperes, without any appreciable loss of electricity.
"The points to be aimed at in an accumulator are longevity and energy, or, rather, rapid yield per kilo. ”

“ This may be conveniently done by inserting in one of the charging leads an incandescent lamp which will pass the required quantity of current. If the current required be as large as 10 amperes, a suitable resistance or 10 lamps in parallel, each passing one ampere, may be used. Great care should be taken to see that the battery is connected properly. ”

“ Theory of the Arc Discharge.—An incandescent body such as a piece of carbon even when at a temperature far below that of the terminals in an arc, emits corpuscles at a rate corresponding to a current of the order of 1 ampere per square centimetre of incandescent surface, and as the rate of increase of emission with the temperature is very rapid, it is probably at the rate of many amperes per square centimetre at the temperature of the negative carbon in the arc. ”

“ The energy of any current is determined by and is equal to the product of two of its properties, its volume or ampèrage and its pressure or voltage. Letting C represent the ampères and V the voltage, we have that the energy C V. In passing any current over any wire there is a loss of voltage determined by and equal to the product of two things—i. e., the ampèrage of the current and the resistance of the wire ”

“ If an alternating current is to produce in a given wire the same amount of effect as a continuous current of 100 amperes, since the alternating current goes down to zero twice in each period, it is clear that it must at some point in the period rise to a maximum greater than 100 amperes. How much greater must the maximum be? ”

“ Ten amperes, through a resistance of sixty ohms, which is as low a resistance as we may expect in a fibroid, means a force of six horse power, this in electro-chemical force or heat would destroy the abdomen in a few momenls. Any unlucky fireman who for a moment touches non-insulaled parts of a wire carrying a ten ampere current is struck dead, and yet one enthusiastic electro-therapeutist claims to have applied a currenl of ten amperes to a living woman! ”

“ Avoid overloading an over-compounded machine. Since its voltage is raised automatically, its output in watts is increased a similar amount at the switchboard, and, for a given resistance, its output in amperes would be increased the same amount, as can be ascertained by applying Ohm's Law. Your ammeter is the best guide. Your machine is built to stand a certain number of amperes, and this should not be exceeded in general practice. ”

“ Fig. 75 shows a voltmeter V, and ammeter A, so placed in the circuit that readings can be taken. D represents a dynamo. A is placed so that the whole current passes through it, while V is placed between the main wires to measure the difference in potential. The product of the two readings in volts and amperes gives the number of watts. ”

“ Since one horse-power is equivalent to 746 watts of electricity, we have, if we could generate it without loss, said the boys, nearly the equivalent of 6 kilowatts of electricity, or about 54 amperes at 110 volts. ”

“ Amperes of electricity are analogous to gallons of water. It is possible to have exceedingly high voltage of electricity without amperes enough to do damage. When one holds his finger near to a rapidly moving leather belt and a stream of sparks passes between the finger and the belt, the voltage may be 50,000 or even [177] 100,000, but the quantity in amperes is too small to do any damage or even produce much sensation. A similar thing is true when one produces sparks by rubbing a cat's back, or lights the gas by a spark produced by rubbing the feet upon a carpet. ”