# Electric Circuits

1. Oct 2, 2013

### sevag00

1. The problem statement, all variables and given/known data

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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2. Oct 2, 2013

### Simon Bridge

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.

3. Oct 2, 2013

4. Oct 2, 2013

### Staff: Mentor

Show how you would determine the potential of the controlled source on the left.

5. Oct 2, 2013

### sevag00

ib=8A, Vx= ib/4 = 8/4=2V

Last edited: Oct 2, 2013
6. Oct 2, 2013

### Staff: Mentor

Check the defined direction of ib. Is the 8 A source really driving current in the direction indicated?

7. Oct 2, 2013

### sevag00

Oh. You mean they are in opposite direction. So the current ib is negative, right?

8. Oct 2, 2013

Right.

9. Oct 2, 2013

### sevag00

Good. Thanks for the help.