Kirchhoff's Current Law, Junction Rule, KCl Circuits - Physics Problems

in this video we're going to talk about kirchhoff's current law abbreviated kcl so the basic idea behind kirchhoff's current law is that the total current that flows into a junction must equal the total current that flows out of the junction so if we assign the current values that flow into a junction let's say if we make it positive and the current that leaves the junction negative then in that case the sum of all of the individual currents must add up to zero if we assign it that way so if we have 10 amps going into the junction and 10 amps coming out if the positive 10 that's going in and if we add that to the negative 10 that's going out it has to add up to zero now let's work out a basic example so here's the junction let's say if we have 10 amps of current and the current flow in this branch let's say it's 14 amps and once again we're going to call this i1 and i2 so go ahead and calculate i3 so first we need to determine if the currents are positive or negative so this current the 10 amp current is entering the junction so that's a positive current the 14 amp current is leaving the junction so that's negative so we can say that i1 plus i2 plus i3 adds up to zero i1 is 10 i2 is negative 14 . now let's calculate i3 so 10 minus 14 is negative 4 . now we need to take this number move it to that side where it's going to be positive 4 . so i3 is equal to positive 4 amps because it's equal to a positive value this time the current is flowing into the junction