02 PSC rev F09 - EECS314/ Deni2onsandUnits...

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EECS 314 // Passive Sign Conven2on 9/1/10 © 2010 A. Ganago 1 © 2010 A. Ganago 1 Power in Electric Circuits. Passive Sign Conven2on Defini2ons and Units Power can be absorbed (dissipated) or supplied (delivered) Passive sign conven2on for bookkeeping: absorbed power is posi2ve; supplied power is nega2ve Conserva2on of power in circuits: the total power equals zero PSC rev F09 © 2010 A. Ganago 2 Defini2ons and Units (1) Voltage difference V is work on a unit electric charge Current I is number of charges moved per unit 2me Thus V∙I = work on all charges moved per unit 2me = Power PSC rev F09 © 2010 A. Ganago 3 Defini2ons and Units (2) Power = Voltage ∙ Current 1 volt ∙ 1 coulomb = 1 joule 1 amp = 1 coulomb / 1 sec (1 volt) ∙ (1 amp) = 1 joule/sec = 1 waW 1 V ∙ 1 A = 1 W PSC rev F09 © 2010 A. Ganago 4 Power can be either supplied or dissipated (1) In simplest circuits, we can easily see which element consumes power and which one supplies power In a flashlight, the baWery supplies power and the lamp absorbs it The current enters the posi2ve terminal of the lamp and the nega2ve terminal of the baWery PSC rev F09 © 2010 A. Ganago 5 Power can be either supplied or dissipated (2) During a jump start of a car, how can we determine which baWery supplies power and which one absorbs it?
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