Eli5: How high voltage (lightning, HV charged metal sphere) discharge to earth without earthing, while battery requires both terminal to complete circuit?
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When the voltage is enough, current flow through the air. It’s about 3000 V/m, give or take, for air.
So if you had a battery with a voltage of 30 kV and you held the electrodes 1 cm apart, the air would break down and current flow from one terminal to the other.
The same happens with lightning, just at much higher voltage. At a cloud ceiling of 100m you need 300 million Volts to break down the air. Which is what a typical lightning bolt actually has. A lightning bolt is what happens when the breakdown voltage between the cloud amd ground is exeeded, at that point the air (in a thin channel) suddenly becomes conductive and shorts to ground, and at 300 milliom volta, that short circuit to earth leads to a **massive** rush of current of 30 000 Amps which turns the air into a 28 thousand °C super bright lightning, which is the flash you see.
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