# Potential difference

1. Jun 5, 2012

### kalupahana

1. The problem statement, all variables and given/known data
The Cells in a circuit has 2V and 4V emfs and 2Ω and 6Ω internal resistance respectively. Find the potential difference between AB

2. Relevant equations
V=IR
Kirchoff's Laws

3. The attempt at a solution
The attempts are in image

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2. Jun 5, 2012

### Metaleer

AB seems to be a shortcircuit. That is a potential difference of 0, so if you end up getting that, it's nothing to worry about. If you got something other than 0, that's when you should be worried.

Basically, you can think of a shortcircuit as taking a branch with a single resistor R, and doing R → 0. From V = IR, you see that I = V/R, so if R → 0, the only way to stop I from going to infinity and being a defined finite value, is to have V = 0, that is, the potential difference across a shortcircuit vanishes.

3. Jun 5, 2012

### SammyS

Staff Emeritus
If VAB ≠ 0, then it would be I-i that goes to infinity.

4. Jun 6, 2012

### Metaleer

The I in my explanation was the I of an arbitrary branch in which a shortcircuit is produced, I didn't use the same circuit as the one given. That's why I said V = IR, and not V = (I-i)R.

The I of my example would be extrapolated to whatever it need be, per particular circuit.

5. Jun 6, 2012

### kalupahana

Ok thanks for help, i got it

6. Jun 6, 2012

### Metaleer

You're welcome.