A very simple question about ohms law

kiloman

Joined Sep 30, 2009
5
hey everyone

i was going over my basic electronics from scratch, and i was going over ohms law. well i understand the simplicity behind the law and how voltage, current, and resistance are all related, but i started thinking about what if resistance was 0... so there would be no voltage or current right? well when i try to visualize this, 0 resistance would mean there is no resistance for the electrons to pass through. so how can there be no voltage or current? like if we took a copperwire and connected it from the + to the -, then it would be a short circuit. wouldnt there be a voltage and current still? even if for a brief period of time before something bad happens? maybe im thinking the wrong way? let me know! thank you

Voltboy

Joined Jan 10, 2007
197
In the case of the copperwire short circuit, there IS resistance, little but there is.
It happens that a superconductor has almost 0 resistance, so little that its negligible, and that's why it is so interesting and many researchers are trying to find a way to create superconductors at normal temperatures. I actually don't know how Ohms law applies to superconductors, try a google search for it.

wr8y

Joined Sep 16, 2008
232
what if resistance was 0... so there would be no voltage or current right? well when i try to visualize this, 0 resistance would mean there is no resistance for the electrons to pass through.
In a real world circuit, if you applied any voltage to a resistance of zero ohms, you would have no voltage across the zero ohms, but your current would soar to the maximum value the battery or other source is capable of supplying. (That is to say, the current would be limited by the "internal resistance" of the source).

The only limit on the current would be how much current it takes to burn your conductors open OR, again, the maximum amount of current the supply can supply.

Wendy

Joined Mar 24, 2008
21,840
Pure theory, you would have infinite current and zero volts. Same thing you get whenever you have zero in a algebretic equation. Somewhere there would be resistance though, if only in the battery (and right before it explodes into a ball of fire).

bountyhunter

Joined Sep 7, 2009
2,498
hey everyone

i was going over my basic electronics from scratch, and i was going over ohms law. well i understand the simplicity behind the law and how voltage, current, and resistance are all related, but i started thinking about what if resistance was 0... so there would be no voltage or current right? well when i try to visualize this, 0 resistance would mean there is no resistance for the electrons to pass through. so how can there be no voltage or current? like if we took a copperwire and connected it from the + to the -, then it would be a short circuit. wouldnt there be a voltage and current still? even if for a brief period of time before something bad happens? maybe im thinking the wrong way? let me know! thank you
There is zero resistance in superconductors at temps of absolute zero. There would be current flow, but there would be no voltage developed across the resistance because there is none. In effect, you can have current flow without any electromotive force (Volts) to push the current.

It sounds impossible, but that's what relativistic physics predicts and it has been demonstrated.

TheWeasel

Joined Aug 28, 2009
4
hey everyone

i started thinking about what if resistance was 0... so there would be no voltage or current right? well when i try to visualize this, 0 resistance would mean there is no resistance for the electrons to pass through. so how can there be no voltage or current?
For this part of your query, I'm sure you could have 0V = 0I x 0R by having a supercooled silver 'ring donut' as a circuit with very close to no resistance, passing no current, because there's no voltage difference anywhere in the 'circuit'.

For your other point, I agree with other posts....i.e a big spanner across your car battery terminals would end badly, but for the microsecond before the spanner explosively melts, the current would be limited (slightly) by the internal resistance of the battery.

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Ratch

Joined Mar 20, 2007
1,068
bountyhunter,

There is zero resistance in superconductors at temps of absolute zero.There is zero resistance in superconductors at temps of absolute zero.
Perhaps, but at what current? Could a superconductive material sustain its superconductivity at high current levels? Has absolute zero been reached in the lab yet. I suspect the answer to both the above questions is NO.

There would be current flow, but there would be no voltage developed across the resistance because there is none.
You really mean charge flow. The is a big difference between a infinitesimal amount of resistance and none.

In effect, you can have current flow without any electromotive force (Volts) to push the current.
How would the charge know which way to flow without a voltage present?

It sounds impossible, but that's what relativistic physics predicts and it has been demonstrated.
How does relativity tie into superconductor physics?

Ratch

rjenkins

Joined Nov 6, 2005
1,015
Superconductors are quite widely used in scientific and industrial applications.

There are a few metals that are supeconductors at liquid helium temperatures, and an increasing number of 'high temperature' materials that 'only' need liquid nitrogen.

One common application is superconducting magnets. A coil of superconductor has a connecting / shorting link that can seperately be temperature controlled.
This is warmed, a current is fed through the main magnet coil and once that is at the desired level the shunt link is cooled again. Once the whole thing is superconducting again, the power is disconnected.

The current cannot change without changing the magnetic field, and the interaction between the two is such that they both stay constant for very long times.

A few bits of info: