Unit 1.2 - Passive Sign Convention

# Unit 1.2 Passive - Conventions Sometimes there is more than one Passive Sign Convention valid way to express a physical concept It is handy if

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1 Passive Sign Convention 1 2 Conventions Sometimes there is more than one valid way to express a physical concept. It is handy if everyone does it the same way to avoid confusion. In these situations, it is common to define a standardized convention . The definition of current is an example. We will now introduce another: The Passive Sign Convention 3 The Issue We know that: The battery supplies power Power is negative by definition The lamp dissipates power Power is positive by definition The current through the battery is the same as the current through the lamp. The voltage across the battery is the same as the voltage across the lamp. V B = V L So how do we compute power to get the correct sign? + i v B - - v L i 4 The Ideal Basic Circuit Element It has only two terminals It is described mathematically in terms of current and voltage It cannot be subdivided into other circuit elements i v 1 2 - 5 Current Flow through an Element Since current can’t be stored in our basic ideal elements, the following situations are equivalent v 1 2 i + - v 1 2 i + - v 1 2 i + - 1 2 v i + - 6 Passive Sign Convention The passive sign convention ensures that power is computed in a consistent way There are two cases to consider: Loads - the element is absorbing power Sources - the element is producing power i 1 2 -

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2 7 Passive Sign Convention: Loads The reference direction for current is assigned to enter the positive terminal for voltage.
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## This note was uploaded on 11/01/2010 for the course EE 302 taught by Professor Mccann during the Fall '06 term at University of Texas at Austin.

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Unit 1.2 Passive - Conventions Sometimes there is more than one Passive Sign Convention valid way to express a physical concept It is handy if

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