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# Voltage between two batteries

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#### ratob

##### Newbie level 4
Let's say I get a voltmeter and touch one tip to the positive terminal of a battery and the other tip to the negative terminal of a different battery. The batteries are not connected. I don't understand why voltage is zero. I have read explanations about it being a open circuit, current not being able to flow, voltmeter having a finite impedance and actually measuring voltage drops, etc. but still do not get it.

Can someone kindly attempt to explain it to me? I have a feeling I have a misunderstanding about how a voltmeter measures voltage.

The equivalent circuit of a voltmeter is a load resistor, 10 Megohm for a usual digital multimeter.

If you sketch the circuit comprised of two batteries and a resistor, you'll hopefullly see, that no current can flow through the resistor and thus no voltage can be measured across it.

in any circuit electrons should go out from one side of voltage source and back to the other side. voltage depends on reference like the earth. if you don't have reference you can't measure voltage.

On this circuit if you use voltmeter on wires, you cant measure voltage, because there is no current flow, like mentioned in earlier posts.

In this design you can measure voltage on wires with voltmeter, and should be around 24V for 12V lead batteries.

Hi.

Will this explain?

Lets say that Mars is a habitable planet in a housand years from now, and there is water, mountains and walleys there. Just as on earth.
Then you ask - how much water would flow between the bottom of the sea on Mars to the bottom of the sea on Earth if there was a tube between?

How to answer that?

Well - it won't flow as much as a drop of water. No way, no nothing. The tube (if ever built) contents will remain cacuum.

It would forever be two separated systems. Just as it is for two batteries that is not connected.

Well - it won't flow as much as a drop of water. No way, no nothing. The tube (if ever built) contents will remain cacuum.

One correction there is flow of material between planets, we have lots of meteorites from Mars on Earth, and in some of them there is water.

Mars meteorite 'Black Beauty' contains most water of any found on Earth, say scientists
http://www.guardian.co.uk/science/2013/jan/03/mars-meteor-water-sahara-analysis

An All-Wet Meteorite Arrives from Mars

http://science.time.com/2013/01/04/an-all-wet-meteorite-arrives-from-mars/

Rare Water-Rich Mars Meteorite Discovered
**broken link removed**

http://en.wikipedia.org/wiki/Martian_meteorite

:wink:

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