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Earth ground has a common potential WRT to voltage measurements taken at higher altitudes in the atmosphere (100 V/m3) or something. To measure this difference, you can connect your voltmeter cathode to the Earth and attach the positive lead to a probe electrode at some height.

Is there a way to "bottle" the Earth ground potential so that it would remain at that potential even if placed higher or lower than the positive electrode which sits exposed at its height?

ocrdu
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ClancyJohn
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    Nope. \$ \ \ \ \ \ \ \ \ \$ – Transistor Aug 16 '22 at 20:02
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    Yeah... Sorry... "Nope" is the right answer. You have to understand a voltage is a RELATIVE measure. To have a relative measure, you have to have some physical connection point. If you disconnect the thing that's floating around, it won't have a fixed reference point anymore. In fact, in EE parlance, when something is just floating around, not tied to any particular voltage, we literally use the word "floating" to describe it's voltage potential. – Kyle B Aug 16 '22 at 20:04

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There's a partial answer here.

You can't just do it -- physically, the voltage between to points is the integral of the electric field on any path between those two points.

If you knew the exact path you were travelling on, and had a means of measuring the electric field along that path (see the link, above), then you could integrate the electric field as you traveled. This is subject to all sorts of difficulty involving getting an accurate, unbiased estimate of the field (because otherwise you'll just integrate the bias and get nonsense) -- but it's a way to get the job done.

I suspect you could also measure the voltage between to points that are separated strictly in the vertical direction, and assume that the field varies only vertically. Then you could use the above method, only assume that the only important part of your "path" is the vertical part.

TimWescott
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  • I was trying an experiment where I use a 3.7 Volt battery with its cathode connected to an aluminum hull via 1G-ohm resistor in parallel with a 4F capacitor. I then raised the whole thing up to 40 feet. Maybe another large resistor to the battery anode? The battery potential difference is 3.7 volts. There must be a way to compute an absolute voltage – ClancyJohn Aug 16 '22 at 22:40
  • Maybe an insulated, negatively-charged material attached to the hull via capacitor could be a reliable "ground" WRT to altitude – ClancyJohn Aug 16 '22 at 22:51
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    There is no absolute voltage to compute. Voltages are, _by definition_ the electrical potential difference between two points. – TimWescott Aug 17 '22 at 00:49
  • @ClancyJohn You should add that detail to your question. It's a little unclear your intent, but what you just said indicates the battery anode is at zero volts relative to the boat hull. It has to be because ohms law dictates V=IR.. In your case there is not a complete circuit, ergo I=0, ergo V=0. So the battery anode is at "ground" potential. If you connect ANY resistor less than "infinity" between the cathode and ground, now some current would flow because you have a complete circuit. Note your 'probe electrode' counts as a resistor to ground (no voltmeter has infinite input impedance) – Kyle B Aug 17 '22 at 05:19
  • I placed a 12V negative ion generator(-1KV) inside of a 6" d aluminum sphere. The inside of the sphere was coated with a graphene-based dielectric coat. When I fired it up, I got a negative voltage on the outside hull. This voltage did not change when I changed the altitude of the sphere. If I raise that sphere to an altitude of 40 meters, I'm wondering if that near-infinite resistance between hull and battery cathode will have the atmospheric potential – ClancyJohn Aug 17 '22 at 20:49