SUNY Geneseo, Department of Physics and Astronomy Physics 125: Analytical Physics II Circuit Analysis (Dr. McLean’s Sure-Fire, Never-Fail Technique) Getting minus signs wrong is the plague of circuit analysis. There are many choices for systems to try to keep the minus signs under control. Unfortunately, no matter what system you choose, there is always some circuit for which the system seems inconvenient or non-intuitive. If you try to switch to the “most intuitive” system for each circuit, you will most likely get confused sometimes. So I recommend choosing one system and sticking with it, even when it is a bit awkward. Here is the system I recommend. 1.For each circuit element, choose a direction which you will call “the positive direction”, and indicate with an arrow. Each element has its own ∆V, i, and (for capacitors) Q. a.Positive imeans charge carriers (with positive electrical charge) moving in the direction of the arrow.
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Electric charge, minus signs, Analytical Physics II, Department of Physics and Astronomy, arrow points, means positive charge