This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...electric quantities be measured in practical units. A volt coulomb is therefore identical with one joule. Electric power is the time rate of expenditure of electrical energy, or Electric Power = EI (322) One volt ampere is identical with one watt. A kilowatt is 1000 watts. In commerce, the unit of energy used is the ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...electric quantities be measured in practical units. A volt coulomb is therefore identical with one joule. Electric power is the time rate of expenditure of electrical energy, or Electric Power = EI (322) One volt ampere is identical with one watt. A kilowatt is 1000 watts. In commerce, the unit of energy used is the watt hour = 3600 joules, or the larger unit, the kilowatt hour = 1000 watt hours. If it be desired to measure the heat in calories, produced by the absorption of electrical energy, we have, since one joule equals 0.24 calorie (Art. 177), H = l2Rt joules = 0.24 IBt calories (323) where all electric quantities are measured in practical units. CHAPTER XXXIV OHM'S LAW AND ITS APPLICATIONS 270. Ohm's Law. Ohm1 found in 1827 that the resistance of a given conductor is independent of the magnitude and the direction of the current flowing through it. Equation (320), in which we have made this assumption, is therefore called Ohm's law. It is frequently written in the equivalent form j, -r, B The current flowing through a conductor is proportional to the difference of potential and inversely proportional to the resistance of the conductor. This law holds for all constant currents or currents whose strength changes very little in course of time. 271. Kirchhoffs Laws.2, First Law. If several conductors Fio. 143. meet at a point, the algebraic sum of all the currents flowing toward the point is zero. A current flowing from the point must be taken as negative. Thus, in (Fig. 143), V h J J1 + 72-/3-74 = 0 (324) or, in general 27= 0 (325) Kirchhoff's first law simply states that no electricity accumulates at any point of a closed electric circuit. In a simple circuit the current is the same, no matter in what part of the circuit the current is measured. 1Ohm, Di..
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