bq). Difference: the other dome is grounded, so when the spark occurs, the HV dome is suddenly discharged.
But when he points the nail, the current must flow through the resistance of his body, and the charge is being gradually dissipated.
Yes, I think you're right.
bq). (The current though the air then being too small to produce a visible spark.)
(A pointed nail tends to attract the charge better than the rounded dome.) In both cases (I would guess), the same amount of charge is being dissipated over a period of time, i.e. the same AVERAGE current is flowing.
Yes, I think it's that the point on the nail collects charge and concentrates it thus generating a large potential that ionizes the air and provides a current path. It is a much smaller current because there is less charge involved (only the amount of charge that collected on the point of the nail -- not the far greater charge than must accumulate on a flatter surface in order to ionize the same air path (granted a bit shorter, because the nail is closer to the charged globe, but in terms of a lightening rod, not that much difference in distance).
Because it's a much smaller current, it goes unnoticed. It would be an interesting experiment to monitor currents in a lightening rod during a storm.
bq).His equipment may produce 200 kV, but its internal resistance must be so great that only a very tiny current can flow from the dome, so he is never in danger of electrocution.
I don't think this has to do with internal resistance. I think it is merely the amount of charge that builds up before the air ionizes and provides a path for the charge to leak off. The currents in a thunder cloud discharge are so much higher, because there is so much more surface area for charge to accumulate. More charge means higher currents during discharge.
bq). If a lightning conductor could gradually dissipate the charge out of a thundercloud, it would be a quite useful source of power, even if only occasionally !
Yeah, I wonder if this is an untapped energy source? Might be a boon in places like Florida, Central Africa, and Singapore.
I did some more reading on how a lightning rod works and there are three camps:
1. Those that say it works merely by being the highest grounded conductor in the vicinity, thus the best path to ground..
2. That it's point effectively bleeds down the charge thus preventing the strike altogether.
3. That both effects are present and then the bleeding down of charge isn't always enough to prevent a strike, but when it happens, the rod is struck because of it's the best path to ground.
