At 10:52 AM 4/17/2004 -0300, Gerhard Fiedler wrote:

>Actually, I would go a tad further and say that none of the three exists
>without the other two.
>
>>>   - You can have V without I
>
>How would you measure a voltage without having any current flowing -- i.e.
>without relocating some charge carriers?

Electrostatic force is one method.

>If you can't, how can you "have"
>it? In order to have a voltage without a current, you would have to
>postulate a resistance with the value "infinity" -- something possible in
>theory, but not really in practice.

You better hope it's achievable, the program memory storage in your pic works that way.


>Again, how can you measure a resistance without moving any current (charge
>carriers) through the resistance?

It doesn't stop being a resistance when there's no current flowing.

> Keep in mind that the concept of a fixed
>resistance (independent of anything else) is a simplification, helping in
>quick and dirty engineering, but is not correct. A resistance is only the
>proportional constant between the current and the voltage. There is no
>resistance without a current (and a voltage), as the resistance is only
>defined by the relationship between those two.

No.  That's how you MEASURE resistance, but resistance itself is an intrinsic property of the material, the free electron mobility.


>>>   - You CAN'T have I without V and R
>
>Now this one is the only one that's correct.

Yes, you can. Messiner effect in superconductors demonstrates this quite nicely.

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