# series parallel trick question

Discussion in 'Homework Help' started by groundcontrol, Sep 20, 2015.

1. ### groundcontrol Thread Starter New Member

Sep 1, 2015
24
1
Hi there,
I am having trouble getting my voltage drop values across each resistor to add up to the source voltage. I can't for the life of me see where I have gone wrong and its driving me nuts as I'm sure people on here will probably understand.. its driving me insane

If anyone can see the error in my ways I wold be so grateful !?!?

I have attached a 3 pics;
the original circuit diagram (its a trick question - and its working)
my table of values - where something has gone wrong, I've stopped before completing it because it wasn't adding up.
my redraw's in case that's the problem

I hope someone is out there who is up for it, please help?

Thanks

ps pls excuse my hand drawing, I am yet to figure out how to get eagle to put components in on an angle. One thing at a time I guess

2. ### atferrari AAC Fanatic!

Jan 6, 2004
2,838
939
What were you asked to find?

Once you get those 61,5 ohms, what are you suposed to do? Calculate current? You did, so...

3. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,173
1,188
I do not see any error:
Vsup = VR1 + VR3 or VR2 + VR4
Vsup = 10.5V + 13.5V = 24V ??
Vsup = 4.8V + VR4 = ??

Roderick Young likes this.
4. ### JoyAm Member

Aug 21, 2014
112
4
maybe that 390 ma indication confuses you

5. ### groundcontrol Thread Starter New Member

Sep 1, 2015
24
1
Hi ! Yay.. it sounds like this is not going to be an mystery forever THANK YOU hopefully

To my understand thing , the 390mA is the Total current.

IT - VT/RT

IT = 24v / 61.5 ohms = 0.390A

I dont understand what I am missing.. Is there another step beforehand or ??? please?

6. ### JoyAm Member

Aug 21, 2014
112
4
I dont understand what you are missing either since you know what the current/voltage is in every element of your circuit

7. ### groundcontrol Thread Starter New Member

Sep 1, 2015
24
1
Oh.. Jony130, you're right. Whats happened is that I have gone and added up ALL the voltages as if ALL resistors were in series;

R1 + R2 + R3... and obviously ended up exceeding 24volts ,

The answer thanks to you guys for helping me see, is;

VT = Voltage Drop across R1 + R3 = 10.5v + 13.5v = 24v
VT = Voltage Drop across R2 + R4 = 4.8v + 19.2V = 24v

Thank you, well I've managed to be wrong even when I'm right ha, thats gotta be some kind of record heh. Thanks again