# Help with potentials.

Discussion in 'Homework Help' started by devoured_elysium, Jun 26, 2008.

1. ### devoured_elysium Thread Starter Member

Jun 26, 2008
13
0
Hello!

I have two questions:
a) Are those two blue points at the same potential? If no, why? I only have a current generator between them, it'd wouldn't change the potential between them, I guess!
b) We have that tension generator with a difference in the tension at its poles of 12 V. So, may I do what you see in red , in which in one pole(the - one) I set the potential to 0 and the other to 12 V? Or is it wrong? If it's wrong, I'd like to know why!

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2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
Assuming a perfect ammeter, they are. Consider them as points along a piece of wire.

3. ### devoured_elysium Thread Starter Member

Jun 26, 2008
13
0
That is in relationship to a), right? And what about b)?

Thanks

4. ### Sparky AAC Fanatic!

Aug 1, 2005
75
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Is that a current source or an ammmeter?

I was thinking it was a current source and was looking to replace it with it's equivalent resistance at the steady-state values shown.

For example If (big if) you can replace the current source with a 1k ohm then you 0 amps flowing through the Io resistor. You end up with a balanced circuit. In this case the two points would not be at the same potential.

I guess I need to know if it's an ammeter - if so than yes - it would be very very close to the same potential.

5. ### devoured_elysium Thread Starter Member

Jun 26, 2008
13
0
I don't know what it is. I think it is a current generator.

6. ### Sparky AAC Fanatic!

Aug 1, 2005
75
0
If it's a current source then it has a resistance.

(an ideal current source has an infinite resistance and a voltage source has zero resistance - if I remember correctly.???)

if I'm correct on the resistance than there will be a voltage drop across it and then the 2 points will not be at the same potential.

7. ### silvrstring Active Member

Mar 27, 2008
159
0
devoured elysium, you have a voltage source and a current source in your circuit. Use superposition analysis to determine your Vab values for each source. As Sparky said, treat the current source as an open when analyzing the voltage side of the circuit. Treat the voltage source as a short (zero ohms) when analyzing the current source part of the circuit. Sum your two Vab results from each analysis. If the sum is 0 V, the two points have the same potential.

As for the second part of your question, no. Because you have not yet done part 'a', you don't know the total effect your voltage source and current source will have on those nodes.