How do electrons know when a circuit is closed?

Question

I was told that electrons do not begin flowing unless the circuit is closed. The electrons from the battery are not in the ends of wire when it is open, apparently, as there is no reason for them to go there. They do not "test the waters", so to speak. So how do they "know" when the circuit is closed? Also, when do they know? Do they know the instant it is closed? Please resolve this vexing problem for me.

Answer 1

Electrons are fairly dumb, but they do move in the direction they are pushed. When a circuit is closed, assuming there is a functioning battery as you suggest, they suddenly "feel" the battery voltage pulling them toward the positive side of the battery, and simultaneously pushing them away from the negative side.

As for time frames, it is not instantaneous, but pretty quick. The battery voltage is present at both ends of the wire, so its influence is felt throughout the wire. The electrons don't really ramp up to speed, because the wire is full of them, so they all move at once, like a hose full of water when you add another drop.

Answer 2

Go back the the concept of an electric field. Any charged particle experiences a force from another charged particle, or--more generally--whenever there is an electric field.

I recommend first reading this article on Coulomb's Law, and then maybe read up on electric fields.