Electrical Engineering/Kirchoff's voltage law


QUESTION: In solving problems related to Kirchoff's voltage law, that is  to say certain complicated circuits, I'm not being able to understand a small point. How do we find the sign conventions during algebraic sums of products of currents and resistances? To be precise I don't get the ideas related to clockwise and counterclockwise directions of current. How do we know if the current across a resistance is in clockwise or counterclockwise???


ANSWER: It doesn't matter.  So long as you write the equations correctly as you go around the circuit with the same convention in all loops and follow the direction consistently the solution will come out all right.

If you guessed right you will get correct answers.  If you guessed wrong you will get a negative answer.

That is the magic of Kirchoff's law, which says:


See question 7 in the following example:


Good luck with your loop equations.

And here is a good youtube that will give you some clarity:


---------- FOLLOW-UP ----------

QUESTION: Thanks, but I don't understand how to get the conventions in my equation. Please help me with that.

Did you watch the youtube that I suggested in the last answer?  That makes it very clear.

To make it easy, the current always flows out of the plus terminal for electrical engineering cases.  (Some of the electronics teachers and books use the electron flow idea with current flowing out of the minus terminal but that is wrong).  Then if you follow the equation around the loop in that direction you will be okey.  The youtube video uses the plus terminal current flow and it is a good example for a simplified a method.

Here is another good video for the Current Law, but a good one to teach how to write the equations:


Here is another youtube for KVL; this is a good one for you:


Hope this helps.  The last youtube video shows the arbitrary nature or choosing your direction so long as you are consistent in making your equation polarities.  

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