Apply the loop rule to loop aedcba in Figure 21.25.

Video Transcript

This is College Physics Answers with Shaun Dychko. We are going to apply the Loop rule to the loop in this circuit that begins at point a and then goes to point e and then d, c, b and a. So we are traversing the loop in this direction— and I will just highlight the loop in yellow here— we are going to the right through this branch here and we are going to be traversing this resistor R 1 in the opposite direction to the current through it I 1 and when we do that, the potential difference will be positive so there's a plus here... a positive I 1 times R 1 and then we continue up this part of the circuit to point d and then across this resistor r 1 to point c and again we are traversing in the opposite direction to the current through it, which is I 2, and so it's gonna be a positive change in potential so that's I 2 times r 1 and then we traverse this battery— this emf 1— from the positive terminal to the negative terminal so that is a drop in potential and that means we have minus emf 1 here and then we continue along back to point a by traversing resistor R 2 and by traversing it in the downward direction, which is opposite to the upwards current, and so it's a positive I 2 times R 2 change of potential there and all of this, after you finish the loop, has to equal zero.