Electric Circuits: Find Vg & Why is it -2V?

AI Thread Summary
The discussion revolves around determining the voltage Vg in an electric circuit, which is found to be -2V. The negative value indicates that the terminals may be incorrectly labeled, with the positive terminal actually having a lower voltage than the negative one. Participants emphasize the importance of correctly interpreting the circuit diagram and the direction of the current ib, which is confirmed to be negative due to its opposite direction. The calculations align with the provided answer key, suggesting that the physics of the circuit configuration leads to the negative voltage. Understanding these concepts is crucial for correctly analyzing electric circuits.
sevag00
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Homework Statement



Hi. I have an electric circuit attached below. The question is to find the value Vg in order for the interconnection to be valid. The answer is -2V.
My question is, why is the voltage minus?
 

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You did the calculation - if you read the diagram correctly you set the [+] terminal to have a higher voltage than the [-] terminal. The minus sign means that the terminals are drawn the wrong way around.
As to "why", you may have done the calculation wrong or maybe that's just the way the physics works out for that configuration.
 
Simon Bridge said:
You did the calculation - if you read the diagram correctly you set the [+] terminal to have a higher voltage than the [-] terminal. The minus sign means that the terminals are drawn the wrong way around.
As to "why", you may have done the calculation wrong or maybe that's just the way the physics works out for that configuration.
I doubt there is miscalculation, because the book had already given the answer key.
 
sevag00 said:

Homework Statement



Hi. I have an electric circuit attached below. The question is to find the value Vg in order for the interconnection to be valid. The answer is -2V.
My question is, why is the voltage minus?

Show how you would determine the potential of the controlled source on the left.
 
ib=8A, Vx= ib/4 = 8/4=2V
 
Last edited:
sevag00 said:
ib=8A, Vx= ib/4 = 8/4=2V

Check the defined direction of ib. Is the 8 A source really driving current in the direction indicated?
 
Oh. You mean they are in opposite direction. So the current ib is negative, right?
 
sevag00 said:
Oh. You mean they are in opposite direction. So the current ib is negative, right?

Right.
 
Good. Thanks for the help.
 

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