Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III KIRCHHOFF'S LAWS Kirchhoff's laws are a development and extension of Ohm's law. They have a wide application in direct and alternating currents, and similar principles are useful in determining the fluxes in some magnetic circuits and the distribution of charges in systems of condensers. They may be stated as follows: I. At any junction the algebraic sum of the currents is zero; that is, the sum of the currents directed toward a junction equals the sum of the currents directed away from the junction. II. In any closed electric circuit the algebraic sum of the impressed e.m.fs. and the reactive e.m.fs. equals the algebraic sum of the dissipative voltages. For steady direct currents this may be simplified as follows: In any closed electric circuit the algebraic sum of the impressed e.m.fs. equals the algebraic sum of the ohmic drops. In applying these laws to the solution of problems involving electric circuits the following simple conventions will be found very useful: 1. Place one arrow on each branch to show the direction of the current assumed in that branch. This arrow may be placed at will. Then at any junction the currents towards the junction will be called positive and those away from the junction will be called negative. The algebraic sum of the currents at any junction is zero. If in the solution of a problem the value of a current is positive the arrow shows the actual direction of the current, on the other hand, if the value of the current is negative the actual direction of flow is opposite to the direction of the arrow. 2. Indicate by plus ( + ) and minus ( —) signs the direction in which each e.m.f. acts or is assumed to act. When passing through an e.m.f. from — to + (a rise in voltage) call it positive, and when passing through an e.m...