Determine each node voltage in this series/parallel circuit Please(:

Discussion in 'Homework Help' started by Logan Negus, Jan 24, 2017.

Jan 24, 2017
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2. LesJones Well-Known Member

Jan 8, 2017
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Simplify the circut so it just looks like 3 resistors in series. I assume this is homework so I will just give you that hint. You would learn nothing is I just gave you the answer.

Les.

Last edited: Jan 24, 2017
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3. Logan Negus Thread Starter New Member

Jan 24, 2017
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I get a 200 ohm resistor when you simplify the parallel part, but my concern is that does the resistor get placed on the left or right side of the "A" node

4. ErnieM AAC Fanatic!

Apr 24, 2011
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A big hint is the three resistors from battery to B can be replaced by a single equivalent resistance.

5. Logan Negus Thread Starter New Member

Jan 24, 2017
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I got 200 ohms for the resistor at A but whatever i do to find Va, Vb, Vc doesnt make sense

6. WBahn Moderator

Mar 31, 2012
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Don't worry about maintaining the integrity of Node A (or any of the nodes) for now. First find the total amount of current flowing in the battery. Once you know that you know the current in some of the resistors and can walk the voltage drops from a known voltage (one side or the other of the battery) to one of the nodes to find the voltage at that node. Do that for as many nodes as you can. Then use that new knowledge to tease out the rest of the voltages.

For instance, if you already knew the voltage at B (say I told you what it was), could you use that information, without knowing any of the currents in the circuit, to figure out the voltage at Node A?

7. ErnieM AAC Fanatic!

Apr 24, 2011
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Correct!

Now you have three resistors in series, 200, 100 and 100 ohms. Redraw the circuit if you do not see that. (If you've been at this as long as some of us the circuit redraws itself for you.)

8. Motanache Member

Mar 2, 2015
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"Now you have three resistors in series, 200, 100 and 100 ohms."
Now you have two resistors in series, 200, 200 ohms.And Vb between them.
So Vb is half the supply voltage Vb= 6V.
Vc is half this 6V, so Vc=3V.
Va it is between R1=100ohms and R2=300ohms:
R1 have a quarter and R2 have three-quarters form a voltage difference between V+ and Vb, that is 6V.
6/4V on R1 => Va=12V-1.5V

Please check the solving, I wrote in haste.
But this is not the way to solve. you have to apply the formulas and learned rules.

Difference between V+ and Vb =6V

9. ErnieM AAC Fanatic!

Apr 24, 2011
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Giving an answer, especially without explanation, teaches nothing.