# Finding unknowns in a Series/Parallel Circuit

#### MrGR

Joined Jan 26, 2008
3
We have studied series and parallel circuits in our class. We have been given an extra credit problem that consists of a series-parallel circuit that we are to find the unknowns. I have attached a copy of the problem. I am not looking for answers, just some guidance as to how I can attack it. Any help is greatly appreciated

#### Attachments

• 29 KB Views: 57

#### thingmaker3

Joined May 16, 2005
5,084
The first thing I would do is to re-draw the circuit. I would try draw it in a way to make obvious which resistors tie to battery + and - and are therefore in parallel.

I would then solve any series resistances as equivalent resistance. Next I'd do the same for the parallel resistances.

#### MrGR

Joined Jan 26, 2008
3
Thank you for your suggestion, thingmaker3. I'm not sure why, but I am really struggling with getting this simplified. It's embarrasing because I know that this isn't a real complex circuit. I know how to use Ohm's Law, KCV, and KCL. If someone could help me with simplifying the circuit I would appreciate it.

#### S_lannan

Joined Jun 20, 2007
246
when tackling something like this i look for groups of known things that can help find an unknown thing.

eg - we know the value of r1 and r2.
we know that kvl states that Vsupply = vr1 + vr2

so if we simplify that series loop by adding r1+r2 we can find the current going
through that branch by using ohms law

I = Vsupply / (r1+r2). ----> I = 10/1100 ------> I=9.09mA

now that we know the current going through those two resistors we can
figure out how much voltage drops across them.

Hope that demo helps...

#### MrGR

Joined Jan 26, 2008
3
I have worked through this problem the best that I know how. I would greatly appreciate it if someone would look over my worksheet and check my logic. I would like to thank everyone in advance for their help and encouragement.

#### Attachments

• 32.5 KB Views: 29

#### JoeJester

Joined Apr 26, 2005
4,310
MrMG,

You did make some errors.

Attached is my calculations.

#### Attachments

• 54 KB Views: 33