# Short circuit question

• May 4th 2008, 08:07 PM
topsquark
Short circuit question
I had a student ask me this question. I have never seen two sources connected in parallel quite like this so I thought I'd see if anyone with more knowledge about circuitry could verify my thoughts.

The parallel combination of sources sets up a short-circuit in the system, with a "back" current balancing out to produce an overall 3 V potential across the resistor.

Obviously in reality the sources have internal resistance and the problem is easily solvable. It's the zero internal resistance case I am curious about.

-Dan
• May 4th 2008, 08:14 PM
Isomorphism
Quote:

Originally Posted by topsquark
The parallel combination of sources sets up a short-circuit in the system, with a "back" current balancing out to produce an overall 3 V potential across the resistor.

I did not understand the "back" current idea, can you please elaborate?
• May 5th 2008, 03:28 AM
topsquark
Quote:

Originally Posted by Isomorphism
I did not understand the "back" current idea, can you please elaborate?

My thought is that the 5 V source will cause a current in the 2 V branch in the "wrong" direction. (That's what I'm calling a "back" current.) Normally when this happens we have an effective cancellation of the 2 V potential leaving a leftover of an effective 5 V - 2 V = 3 V potential over the parallel combination. (I think I'm remembering that right.)

-Dan