Then I jump over \$V_b\$, encountering another rise in potential as I go, so I add again. My next leg of the journey is across R1, where I detect a drop in potential, as the authors have kindly told us will be the case, with those signs, so I will subtract \$V_1\$. Starting at the bottom left, where I arbitrarily "declare" the potential to be zero volts, going clockwise, I first cross \$V_a\$, which entails a rise in potential, so I add. Here I apply KVL by adding when I see a rise in potential, and subtracting when I see a fall in potential as I traverse each element. Simulate this circuit – Schematic created using CircuitLab Adding and subtracting while traversing the loop I'll redraw the circuit here, with labels so the algebra makes sense: I'll take that approach here, so you can appreciate what I mean. This entails adding each term, regardless of polarity, and then afterwards, when plugging in all the known values, we set the sign of those knowns to be consistent with the direction we travelled.Īlternatively, we can take the approach where if we do know the polarity of voltage across some component, we account for drops in voltage as we travel over it by subtracting, and we account for rises in potential by adding. The approach I usually advise is that one does not take into consideration polarities when traversing all the elements in a loop, and that we rely on the signs of the resulting solution to reveal actual polarity.
![solve elec setup solve elec setup](https://i.pinimg.com/originals/8d/e0/40/8de040af8596afc7edd6feaf58e6f10a.jpg)
Using KVL sounds easy, but polarities can really mess you up.