I'm very confused here! Most of the times I'm getting wrong answers or impossible equations because of this - even if I know the procedures for the analysis. It has to do with setting up nodal analysis and current flow direction.
In this example (image below), the tutor told to "consider" the current always going outwards from node 1 and node 2 - even if that's not the true behaviour for the current - because the sign will be taken care by the numerical value. Fair enough.
- First he considers it for node 1 as he just explained. Every current is going "outwards" from the node: including the current that goes directly from node 1 to node 2.
- But by the node 2 he ALSO considers the same current going "outwards". Meaning, from node 2 to node 1. How can the set of equations be consistent if the current cannot be both going from 1 to 2 and from 2 to 1? How is this system of equations possible?
- Then he considers the current imposed by the current source to flow into node 2. Now the direction matters? Wouldn't just the sign be taken cared of?
I'm very confused about all of this sign. Do we have to be consistent or not? Why is he able to do that? How can I always get away with the signs when doing nodal analysis reducing mistakes?
Thank you in advance!