On Fri, Nov 28, 2008 at 04:13:21PM -0500, Andrew Reid wrote: > On Friday 28 November 2008 14:10, lee wrote: > > Is it even possible to measure a mere potential? > > You mean, in principle? Of course. > > Put your two wires of unknown potential difference at > opposite ends of an evacuated tube. Arrange the geometry > so that the electric field between them is linear in space. > You can do this by hooking them up to big plates and putting > the plates close enough together, making basically a > vacuum capacitor. > > Then, shoot charged particles into the space between > the electrodes. From the way they deflect, and their > charge-to-mass ratio, you can deduce the electric field > strength, and from that, the potential difference between > the electrodes giving rise to the field. > > Alternate method: Place a piezoelectric crystal of > known characteristics in the gap, and measure the > change in shape. From this, you can deduce the degree > of polarization, and thus the externally-applied field, > and from that, again, the voltage difference between > the electrodes.
It takes energy to defect particles or to change the shape of a crystal, doesn't it? You would be observing/measuring effects and *deduce* that there is a potential, but that is different from observing/measuring the potential itself, isn't it? -- "Don't let them, daddy. Don't let the stars run down." http://adin.dyndns.org/adin/TheLastQ.htm -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
