Thévenin's theorem: Difference between revisions

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Line 22: The Thévenin-equivalent resistance ''R''<sub>Th</sub> is the resistance measured across points A and B "looking back" into the circuit. It is important to first replace all voltage- and current-sources with their internal resistances. For an ideal voltage source, this means replace the voltage source with a short circuit. For an ideal current source, this means replace the current source with an open circuit. Resistance can then be calculated across the terminals using the formulae for [[series and parallel circuits]]. This method is valid only for circuits with independent sources. If there are [[dependent source]]s in the circuit, another method must be used such as connecting a test source across A and B and calculating the voltage across or current through the test source. Note that the replacement of ~~voltage~~q1voltage and current sources do the ''opposite'' of what the sources themselves are meant to do. A voltage source creates a difference of electric potential between its terminals; its replacement in Thévenin's theorem resistance calculations, a short circuit, equalizes potential. Likewise, a current source's aim is to generate a certain amount of current, whereas an open circuit stops electric flow altogether. ===Example=== [[Image:thevenin-~~example~~ex ample-png.png\|thumb\|left\|upright=2.9\|1. Original circuit <br>2. The equivalent voltage <br>3. The equivalent resistance <br>4. The equivalent circuit]] {{clear}} In the example, calculating the equivalent voltage: