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Unformatted text preview: . This process will become clear when we start solving circuits, so you don’t need to worry about it now. 2) There are circuit elements that do not consume power and so it becomes awkward to keep saying: “it consumes – A watts”. For example sources are elements that usually PROVIDE power to the circuit. Therefore in sources we follow the active sign convention: 15.7 In this case we say that the source provides power P = VI. Of course it is still OK to use the passive sign convention and say that the source CONSUMES –VI watts. It is the same thing! Conservation of Power = always need to be satisfied in solving a circuit One last thing we need to understand is the fact that power is conserved (as expected) in a circuit. Therefore Pprovided Pconsumed There are other ways you can express this mathematically (look at the book for example), but the important thing it to understand that it holds and how to apply it. The book has some good examples that you could study. Resistance (we have already seen it from the electromagnetic point of view) Ohm’s law: In 1827 Ohm noticed experimentally that I V. He called R the constant of proportionality and therefore he got: Ohm ' s law V RI The constant R is called “resistance” and has units of V / A . A material has 1Ω resistance if a voltage drop of 1V causes a current of 1A through the material. Notice that the resistance R is (ideally) independent of the voltage V and current I. This is fairly close to the reality of many practical resis...
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This note was uploaded on 03/06/2014 for the course ECE 201 taught by Professor All during the Spring '08 term at Purdue.
- Spring '08