# Kirchhoff law + Ohm Law = headache

Discussion in 'Homework Help' started by Bigcountry, Jan 15, 2009.

1. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
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I thought I would be original with a title and humorous also. which after trying to figure out all this problem has driven me crazy.

I tried the product over sum rule and it didn't seem to work and I got it all screwed up on superposition. so maybe someone can get me get the problem #3 started.

thank you for all your help or insight.

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2. ### guitarguy12387 Active Member

Apr 10, 2008
359
12
Couple ways you could do it.

You could reduce the circuit to one resistor quite easily and determine the total current. Then open the circuit back up and use ohm's law/KCL to determine the needed current's/voltages.

In general, i personally tend to use KCL pretty much all the time though cuz i'm most comfortable with it. So i see 2 unknown nodes. You could just write KCL equations at those nodes and solve those 2 equations by a simple substitution.

Hope that helps get you started!

3. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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Even better equation: Progress=Pain

eric

4. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
71
0

I got .2 A for the total current by reducing the circuit to one resistor. ok now what do you mean by "opening the circuit back up"?

5. ### guitarguy12387 Active Member

Apr 10, 2008
359
12
I just mean sorta work backwards. Reverse the resistor combinations (that is, turn those combined resistors back into series/parallel resistors) one by one while calculating currents and voltages.

Does that make sense?

If not, i can draw it out for you... sorta illustrate what i mean.

6. ### MareBear Member

Oct 29, 2008
22
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Last edited: Jan 16, 2009
7. ### Bigcountry Thread Starter Active Member

Jul 4, 2008
71
0
ok so that I found the total current is go back and work it and find the voltage at each series/parallel then in turn find the current at each one??? I am starting to get what you did but I am struggling here. thanks for your help thus far.. i have almost got it.

so I take the total at each parallel and then find the voltage then the current ?

8. ### MareBear Member

Oct 29, 2008
22
0

you use current divider to find the current at each one and with that you can find the voltage