We all know lightning travels through the path of least resistance.
Letâ€™s say we zoom in on the electricity thatâ€™s flowing downwards, and see what it does every 1 nanosecond (it travels about 1 foot in this time period). The flow of electrons gets to a point, and it has to find the path of least resistance to keep going. For simplicity, letâ€™s say it has 1 of 3 options. How does it know which to choose? Clearly, it doesnâ€™t have â€œsensesâ€ to figure this out. If you know your electricity, you know it doesnâ€™t â€œprobeâ€ its different path options until it finds the best way to go. So, how does it know?
A semi-comparable system would be water flowing down a hill. If the water gets to a place where it must choose to go 1 of 3 ways, most of it will go down the steepest path. But some of it will still go down the other two.
Electricity is different. If +10V gets to an intersection, and has to choose between 1 of 3 equally resistive paths (letâ€™s say 250 ohms for the heck of it), one going to +7V, one going to +5V, one going to ground, ALL of the current will go right to ground. Nothing will go down the other two paths. Voltage (potential) difference is just like â€œsteepnessâ€ of a hill in this example.
So, how does it know?
Sander, the problem is that neither your lightning description, nor your analogous “river” scenario, is representative of the system under question. If they were, you would have a valid point.
However, the truth is a bit more subtle than that.
I had to consult with some Electrical Engineer friends to come up with a way to explain this.
The idea that lightning flows downwards from the cloud to the ground, is the problem. What really happens is this: the storm creates a potential difference between the charge of the clouds and the charge of ground. When the potential becomes greater than the resistance of the air, the electrons flow OUT OF GROUND to the cloud. That’s why no electrons end up on either of the other paths (in the circuit example) – they didn’t come from there.
It’s more convenient to think of electricity flowing to ground, but it’s more accurate to describe it as flowing FROM the path of least resistance than DOWN the path of least resistance.
At least, that’s what my sources tell me.