Combined Series and Parallel circuits

Thread Starter


Joined Aug 29, 2007
Can anyone help explain how the the following formula is worked out as i cant seem to get my head around it?

There is a 12v supply which is met with a series resister (R3) of 4 ohms, which is then followed by 2 parallel resister (R1) with 10 ohms & (R2) with 40 ohms, the current is 1A.

Can someone help explain the following:

1. How the 1A is worked out?
2. How the voltage passing through each resister is worked out?
3. How the overall resistance for the circuit is worked out?

Any help would be great.

Many Thanks



Joined Apr 20, 2004
The one amp current gives you the key. By R = E/I, you get Rt for the circuit. The voltage drop across R1 lets you get the voltage across the parallel resistors.

Thread Starter


Joined Aug 29, 2007
Thanks for your quick resposne, would you be able to provide me with a more detailed breakdown of how the formula works?



Joined Apr 2, 2007
try searching about resistances in parallel to get its eq resistance.
then add the eq in parallel to series resistance--there u go overall resistance..
then apply ohm's law with supply voltage and overall resistance.--there u go 1A.
now current is known. use ohm's law again to get voltage drop across first resistor. remaining voltage appears across the two resistors in parallel.
if u want u can apply ohm's law again to find what is the current thru the individual resistances in parallel (it wud sum up to 1A).
i think u should start learning some network analysis if u are to deal with these in future.

edit: ok, the formula for two resistances in parallel is R1.R2/(R1+R2)--but u shud really try to do some work on your own.