Hello, I am having difficulty when trying to solve problems requiring kirchoff's rules. The problem I seem to be having is following the convention used by my book. I can't tell when the current is gaining potential going across a resistor, or atleast going from low potential to high potential. The problem seems to stem from not knowing which end of the resistor is at higher potential than the other, so I can do either +IR or -IR If anyone can clarify, that would be great. Thank you
The current in a resistor always flows from high potential to low potential. So, once you mark the direction of the current through the resistor, the high potential and low potential ends of the resistor become obvious. Generally, when you are solving dc circuits, and you are required to find the current in a resistor, you start by marking the direction of the current. Then, you mark the high potential end and low potential end of the resistor in such a way that the current is flowing from high potential to low potential.
Select your loop. When a resistor is traversed in your chosen loop, along the direction of current, then there is a voltage drop -IR.