# Homework Help: Electrical Circuit Problem

1. Nov 12, 2013

### jendrix

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

The circuit has an unknown component that is a resistor or a voltage source, find which one it is and it's value.

2. Relevant equations

V=IR, KVL, KCL

3. The attempt at a solution

I first used KVL on the outer loop:

14-2I1-10=0

I1=2A

Then on the inner left loop

14-4V-10I2=0

I2=1A

Then KCL to find current through 20ohm resistor of 1A

Inner loop on right hand side

10I2-1x20-?+0

? =-10V

Due to the direction of the current the -10v couldn't be from a resistor as it would result in a positive 10v over the resistor.Instead it must be a -10v source.

Does this look correct? If this was a -10v source wouldn't that disprove all the currents I found?

Thanks

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

2. Relevant equations

3. The attempt at a solution

Last edited: Nov 12, 2013
2. Nov 12, 2013

### Staff: Mentor

Your analysis looks fine. The currents would be fine, too, when the mystery component is a -10V source.

3. Nov 12, 2013

### jendrix

Thank you, so if I understand this correctly, because we knew the 10v across the mystery component and 20ohm resistor this allowed the correct currents to be calculated.Once we knew these currents we could disprove the mystery element being a resistor?

4. Nov 12, 2013

### Staff: Mentor

Yes, that is so.

5. Nov 12, 2013

Thank you