# Homework Help: Circuit source current question

1. Sep 13, 2014

### orangeincup

1. The problem statement, all variables and given/known data
Find is of the circuit below

2. Relevant equations
i=V/R
v1+v2+..=0
is=vs/Req

3. The attempt at a solution
Resistance of circuit as seen by source = 7kΩ
6V(source)/7kΩ(Req)=.857i

My question is, how come i3 is also 0.857i? Shouldn't it be different since it just went through two resistors? Can someone explain to me why the currents are the same? Is it because the resistances are in series?

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2. Sep 13, 2014

### Staff: Mentor

is alone leaves the voltage source, while i3 alone re-enters the voltage source. You can't have one different than the other through the same component...

3. Sep 13, 2014

### orangeincup

If it had another current source or voltage source below one of the resistors, would this still be true?

4. Sep 13, 2014

### Staff: Mentor

There is no way that the current entering a component can be different from the current leaving it. Otherwise charge would be building up on the component or be created or destroyed. Can't happen! Components in series all carry exactly the same current.

If you change the circuit so that i3 is no longer solely feeding the one voltage source but has some other path available (so it feeds into a node shared with the voltage source and something else, perhaps leading to another voltage source), then you no longer have the same setup and that other "something" may contribute to the total current making its way to the voltage source.