On Fri, 16 Jun 2006, Gerhard Fiedler wrote:

> Peter wrote:
>
>> Potential and voltage are one and the same in theory but in practice it
>> is more complicated.
>
> I'm not sure this is on firm ground. I'm no ace in physics terminology, but
> I think "voltage" is a term for the value of an electric field potential,

The definition of potential is 'the energy required to move a punctiform 
charge unit from the point being measured to infinity'. All normally 
measured voltages are *relative* differences of potential, not absolute. 
In this sense a voltage is a potetnial *difference*, but if only a 
potential exists then a voltage must not also exist (until someone 
*measures* the *difference* between that object's potential and a 
reference).

But the definition of the t. voltage is absolute, not relative. Its 
measured version, is relative, no matter what (access to infinity is 
somewhat difficult). So while the t. potential should be there, there is 
no way to measure it as is, it must be measured with reference to 
something else. This implies the need for at least *one* contact or 
quasi-contact. Even the pin/bar proposed by Olin has one contact.

Peter
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