$I_3 = I_1 + I_2$
This is College Physics Answers with Shaun Dychko. The Junction Rule says that all the currents going into a point equals the sum of all the currents leaving that point or that junction. And so this junction here has a current <i>I3</i> going into it. So we have the total of all the currents going in of which there’s only one, so it’s <i>I3</i> equals the total of the currents coming out which is <i>I1</i> and <i>I2</i>. So there’s our Junction Rule written out separately.