The potentials that have to be dealt with are often hundreds and sometimes thousands of volts, and insulation troubles are more serious than is generally appreciated.
At Such Times Gradients Of 400 Or 500 Volts Per Metre Are By No Means Unusual At Kew, And Voltages Of 700 Or Boo Are Occasionally Met With.
He supposes the field near the earth to be ioo volts per metre, or 1/300 electrostatic units.
The electromotive force of each cell is i 07 volts and the resistance 3 ohms. The Fuller bichromate battery consists of an outer jar containing a solution of bichromate of potash and sulphuric acid, in which a plate of hard carbon is immersed; in the jar there is also a porous pot containing dilute sulphuric acid and a small quantity (2 oz.) of mercury, in which stands a stout zinc rod.
The electromotive force of each cell is 2.14 volts, and the resistance 4.
Ohms. The Leclanche is of the ordinary type, and each cell has an electromotive force of I 64 volts and a resistance of 3 to 5 ohms (according to the size of the complete cell, of which there are three sizes in use).
The subjection of the core to a hydraulic pressure of four tons to the square inch and an electric pressure of 5000 volts from an alternating-current transformer has been adopted, by one manufacturer at least, to secure the detection of masked faults which might develop themselves after submergence.
The arc is produced by leading a current of about 5000 volts equatorially between the poles of an electromagnet; this produces what is practically a disk of flame, 62 ft.
Units or 1.112 volts - a close agreement with the experimental result of about 1.08 volts.
A third platinum coil, wound non-inductively between the primary and the secondary, served to carry the current by which the ring was heated; a current of 4.6 amperes, with 16 volts across the terminals, was found sufficient to maintain the ring at a temperature of 11 50° C. In the ring itself was embedded a platinum-thermometer wire, from the resistance of which the temperature was determined.
The Siemens and Halske ozonizer, in form somewhat resembling the old laboratory instrument, is largely used in Germany; working with an alternating current transformed up to 650o volts, it has been found to give 280 grains or more of ozone per e.
17,426 of 1891) uses flat aluminium plates and points, and working with an alternating current of 3000 volts is said to have obtained 1440 grains per e.h.p. hour.
For this purpose the ohmmeter is provided with a small dynamo D, contained in a box, which produces a continuous electromotive force of from 200 to 500 volts when the handle of the instrument is steadily turned.
Hence the resistance of the insulator can be ascertained, since it is expressed in ohms by the ratio of the voltage of the battery in volts to the current through the C C galvanometer in amperes.
With a supply pressure of 200 volts a 5 c.p. carbon filament lamp takes only 0.1 ampere; hence unless a meter will begin to register with 1 1 - 6 - ampere it will fail to record the current consumed by a single small incandescent lamp. In a large supply system such failure would mean a serious loss of revenue.
At first the current is 3000 amperes at 220 volts, increasing to 9000 amperes at 20 volts after 20 hours.
Supposing that the scale under this wire is divided into 2000 parts and that we are in possession of a standard Clark cell, the electromotive force being known at various temperatures, and equal, say, to 1.434 volts at 15° C. The first process is to set the potentiometer.
We can thus measure as described the drop in volts down a known fraction of the whole high resistance and therefore calculate the fall in potential down the whole of the high resistance, which is the potential difference required.
For this purpose a resistance, say, of one ohm is placed in series with the lamp and a resistance of 100,000 ohms placed across the terminals of the lamp; the latter resistance is divided into two parts, one consisting of loon ohms and the other of 99,000 ohms. The potentiometer enables us to measure therefore the current through the lamp by measuring the drop in volts down a resistance in series with it and the potential difference of the terminals of the lamp by measuring the drop in volts down the tooth part of the high resistance of 100,000 ohms connected across the terminals of the lamp.
The electromotive force of the cell diminishes with rise of temperature, the board of trade value being 1.434 volts at 15° C.'
When so made, the cell has an electromotive force of 1.072 volts and no sensible temperature variation.
Electrostatic voltmeters are now almost entirely used for the measurement of high voltages from 2000 to 50,000 volts employed in electrotechnics.
For such purposes the whole of the working parts are contained in a metal case; the indicating needle moving over a divided scale which is calibrated to show directly the potential difference in volts of the terminals of the instrument.
If the wire has a resistance of 300 ohms and is connected to two points differing in potential by 100 volts, the instrument passes a current of one-third of an ampere and takes up 33 watts in power.
The transformer working from a public supply should give about 6000 volts on open circuit, although when the electric flame is established the voltage on the platinums is only from 1600 to 2000.
After the discharge was once started, the difference of potentials at the terminals of the tube varied from 630 volts upwards.
Cryolite is not a safe body to electrolyse, because the minimum voltage needed to break up the aluminium fluoride is 4.0, whereas the sodium fluoride requires only 4.7 volts; if, therefore, the current rises in tension, the alkali is reduced, and the final product consists of an alloy with sodium.
The current is supplied at a tension of 3 to 5 volts per cell, passing through 10 or 12 in series; and it performs two distinct functions: - (1) it overcomes the chemical affinity of the aluminium oxide, (2) it overcomes the resistance of the electrolyte, heating the liquid at the same time.
Each generator can develop 5000 H.P. at a potential of 2200 volts, and is driven by three horizontal double turbines on the same shaft; when working under a minimum head of 32 ft.
They drive electric generators, and the current so produced is taken at a pressure of 22,000 volts on overhead wires a distance of 35 m.
Near the town is a station for reducing the voltage, and current is distributed at 125 volts for lighting purposes and at 500 volts for use on the tramways and for other power purposes.
The formula indicates that the sensibility of the instrument should increase with the charge of the Leyden jar or needle, whereas Hopkinson found that as the potential of the needle was increased by working the replenisher of the jar, the deflection due to three volts difference between the quadrants first increased and then diminished.
He found that when the potential of the needle exceeded a certain value, of about volts, for the particular instrument he was using (made by White of Glasgow), the above formula did not hold good.
At one end is an insulated plate P kept at a potential of 200 volts or so above the earth by a battery.
Wilson found that with the plate electrified to 207 volts and with a tilt of the case of 30°, if the gold-leaf was raised one volt in potential above the case, it moved over 200 FIG.
The jar can be charged so that a certain potential difference V, reckoned in volts, exists between the two coatings.
The safe voltage for most glass jars is about 20,000 volts for glass 1 ' 0 th in.
The size of jar commonly known as a quart size may have a capacity from 4 o 0 th to s 00 oth of a microfarad, and if charged to 20,000 volts stores up energy from a quarter to half a joule or from -ths to Iths of a foot-pound.
By Ohm'S Law, And By The Definition Of Difference Of Electric Pressure Or Potential, We Obtain The Following Alternative Expressions For The Quantity Of Heat H In Joules Generated In A Time T Seconds By A Current Of C Amperes Flowing In A Wire Of Resistance R Ohms, The Difference Of Potential Between The Ends Of The Wire Being E = Cr Volts: H=Ect=Crt=E Z T/R.
Of The Clark Cells To Have In Reality Been 1.4323 Volts, Or About 2 Millivolts Less Than The Value Assumed.
Of The Clark Cell Is Probably Less Than 1.4340 Volts (The Value Assumed By Schuster And Gannon), There Is No Difficulty In Reconciling The Result With That Of Rowland.
313, P. 80, And Found To Be I.4334 Volts, Assuming The Ohm To Be Correct.