Exploring Electric Potential of Lightning Clouds

[mrmojorising]

Opposite charges are built up between lightning clouds and the earth, which creates a potential, which causes lightening.

Say you had a voltmeter that could handle infinite current and with leads hudnreds of meters long, and you stuck one lead onto a cloud which is about to create lightning and the other lead into the Earth -- i assume the voltmeter would read a large voltage.

Now say you stuck one lead into the cloud and the other lead into empty space -- would the voltmeter read 0 voltage or a large voltage? If it owuld read 0 voltage, why is that? The cloud contains charge, so it creates an electrci field againt which it takes work to move a charge, even into empty space some distance away from the cloud, so there should be a voltage recorded?

So if there is a voltage recorded between a cloud which is about to release lightning and empty air why is it that if i put one lead of a voltmeter on a positive terminal of a power supply and the other on a negative terminal i get a voltage, but not if i put one lead onthe positive temrinal and the other in air?

I mean the positive terminal is not only psoitive with trespect to the negative terminal, but also i assume its positive compsared to surrounding vacuum (or air)? I mean it would take work (which implies a voltage) to move a charge form the positive terminal to a point some distance away in a vacuum - just like for a charged cloud, would it not?

 

[DrZoidberg]

If the internal resistance of the voltmeter is high enough there will be a voltage. Even on a clear day you can measure a voltage. About 100V per meter.
The resistance of the voltmeter needs to be extremely high because the current flowing through the atmosphere is very small, except when lightning strikes. An electroscope with a long antenna attached to it might work.
Or maybe a kite with a conductive string attached to a key and a short piece of insulating string at the end to insulate the person from the key. But don't try this during a thunderstorm. It will also work when the sky is clear.

http://www.missioninstruments.com/pages/learning/elec_fields.html
http://en.wikipedia.org/wiki/Natural_electric_field_of_the_Earth