Jul 9, 2011
Medical Student
I used to know this, but I can't find the information any more.

When you add a resistor in parallel:
Req decreases and Voltage decreases
But Current remains constant, and each resistor receives the same current.

When you add a reisistor in series:
I know that Req increases.... but what else happens?
Last edited:
May 9, 2012
When you add a resistor in series, Req increases. Since the resistors are in series, they must receive the same current (even if the resistors have different resistances). The resistors will not always receive the same voltage, unless both resistors have equal resistances and there is nothing else on the circuit. Assuming that the voltage from the battery stays the same, the current decreases, because I = V/Req.

Just a clarification for adding resistors in parallel: Req decreases, and both resistors will receive the same amount of voltage from the battery (which is not always true for resistors in series). The current each resistor gets depends on each resistor's resistance: lower resistance means more current.