# Circuit confusion

## Homework Statement

I am trying to understand the concept of short circuit with kvl laws
it seems like i arrive at contradictory stuff

http://imageshack.us/photo/my-images/38/shortcircuitr.png/
it seems like the voltage across the wire and resistor are equal by KVL
however the current through the resistor is 0
and it so the voltage across it should be 0
but it should be equal to the voltage across the wire
but according to KVL that should be equal to V of the battery which is assumed not to be 0

## Answers and Replies

ehild
Homework Helper
When you short-circuit a battery the current is determined by the internal resistance of the source, and the terminal voltage becomes zero unless the resistance of the wire is comparable to the internal resistance.
In real life, a short circuit will make the battery flat in a very short time and then its emf is zero anyway. And the battery ceases to exist as a battery, as it burns and melts and smells bad ...

ehild

the resistance in this case got shorted , this means the volt source does not see the resistance , and also the current will chose to go through the short circuit not through the resistance , connecting the resistance won't effect the circuit its like it doesnt exist so you can't apply KVL in this case...

When you short-circuit a battery the current is determined by the internal resistance of the source, and the terminal voltage becomes zero unless the resistance of the wire is comparable to the internal resistance.

ehild

huh why would the terminal voltage become zero? if it does then there would be no current right?

so if the r of the wire is more or less than that of the ir, then there would be current, is this what you mean?

so it cannot be examined with introductory physics 2 techniques?

well one thing i dont understand is this if the voltage is 0 then the current is 0 but also voltage is the work required to move a unit of charge between two points so if no work is required shouldn't there be a current?

no potential diff, no current.

can you explain it with work energy theorem concepts?

gneill
Mentor
If the wire is ideal (no resistance) then current can still flow through it with no potential difference across it. It behaves like a single node for the length of the wire.

It's a bit like the situation of a mass falling down a slope and then out onto a flat frictionless surface. The mass doesn't stop moving because it's no longer falling down a slope (falling through a potential difference).