# Current and electricity

1. Jun 4, 2015

### Sagar Singh

Hi there!
as wee all know V=IR
v= potential difference
I=current
R=resistance
so => I=V/R
and somehow we make Resistance almost equal to 0
then I=V/0
will I become infinity?
or what?

what will happen?
Please clear every situation to me?

2. Jun 4, 2015

### ZapperZ

Staff Emeritus
You can't do this. If R=0, then you will not have any potential difference, I.e, you have a short! Current doesn't go to "infinity".

Zz.

3. Jun 4, 2015

### Sagar Singh

Why there will be no potential difference> what is the relation between potential difference and resistance?

4. Jun 4, 2015

### Staff: Mentor

As resistance gets smaller, current gets larger, yes. But there are limits for real systems.

5. Jun 4, 2015

6. Jun 4, 2015

### phinds

Well, lets say you take the output of ALL of the generating stations on Earth. That's going to give you a lot of current capacity. Let's call it 14 zillion amps. OK, now I make R even smaller. Where are you going to get any more current capacity? You can't, so your concept of the equation fails. That's a limit on a real system (and not REALLY a real system, since there are other complications in trying to tie together all the generators on Earth).

7. Jun 4, 2015

### Staff: Mentor

There is also P=IV. Combining that with your expression gives P=V^2/R. So as R goes to 0 so does the power if V is fixed. So the limit is that no real voltage source will actually be able to deliver a constant voltage at arbitrarily low resistance.

8. Jun 4, 2015

### Staff: Mentor

Power goes toward infiniy, but yes: for real sources, internal limitations get in the way (for batteries: internal resistance, for generators: prime mover power capacity).

9. Jun 4, 2015

### Staff: Mentor

We have superconductors thst have zero resistance. We can put a finite current through a superconductor and the voltage difference from one end to the other will be zero. Where is the mystery in that?

We get this question frequently, where people thing that we can set V and I and R to any aribtrary value, and what then? In real life, we can only achieve reasonable value of V and I. R can be measured as the ratio of V to I. No mystery, no infinities.