If we examine our waterflow circuit, we find that any water which flows past the 3rd valve, must first flow past the 2nd and 1st valves. By this we can deduce that the current, or flow of water, is the same past all three valves. At no time can more water flow past one valve than past another. The same is true in electronics. In a SERIES circuit, the current is the same at every point.
Using our previous example of 2 Ω resistors, if we then have a 12 Volt source, what would be our current through the circuit? Let us examine this. We know that because the circuit is series, no matter where in the circuit we are, the current will remain the same. So the problem is, what would be the given current for the complete circuits given voltage and resistance totals? Adding up our 3 resistors, we come to 6 W , and we know our Voltage is 12. So using Ohms Law, we derive this formula: