. Practical wireless telegraphy; a complete text book for students of radio communication . arged by electric dynamos or generators rather than by primary cells. The electromotive force of primary cells varies from .06 to volts accordingto the nature of the battery elementsand the grade of electrolyte. Theelectromotive force of the lead platesecondary cell lies between volts. In electrical equations, potentialor E. M. F. is represented by theletter E. Instruments for measur-ing potential difference are knownas voltmeters. 16. Current Strength and Quan-tity.—Up to this point we h
. Practical wireless telegraphy; a complete text book for students of radio communication . arged by electric dynamos or generators rather than by primary cells. The electromotive force of primary cells varies from .06 to volts accordingto the nature of the battery elementsand the grade of electrolyte. Theelectromotive force of the lead platesecondary cell lies between volts. In electrical equations, potentialor E. M. F. is represented by theletter E. Instruments for measur-ing potential difference are knownas voltmeters. 16. Current Strength and Quan-tity.—Up to this point we have notmade mention of the strength ofthe current or the quantity of elec-tricity flowing through a given cir-cuit. We have simply referred to thepotential difference and the conse-quent electromotive force generatedby chemical cells. Just as we mightuse in the system of hydraulics thegallon per second as a unit to expressthe quantity of water flowing froma given source, so in electrical cir-cuits, we express the quantity ofelectricity flowing by the unit Fig. 5—Simple storage 8 PRACTICAL WIRELESS TELEGRAPHY termed the coulomb. We must not confound the measure of the total quantityof electricity in a given circuit with its strength or rate of flow. The strength ofan electrical current should be described as the rate of flow of electricity througha circuit per second of time. When one practical unit of quantity of electricity(one coulomb) flows every second continuously, the rate of flow or the strengthof the current is said to be one ampere; if three unit quantities flow continuouslyevery, second, the strength of the current is three amperes and so on. Hence wemay define the ampere as the quantity of electricity flowing past any point in acircuit per second of time. The strength of the current in aniperes will be seen to be independent of thelength of time the current flows in a given circuit whether it flows for a fraction ofa second, a minute, or an hour; if the qu
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