Electronic – Two questions about charge between capacitor plates

A Wimshurst machine works by that process.

It puts charge on plates which are close together, then moves the plates apart to generate a high voltage.

When I was at school, in the '70s, a kid made one using PCB material for the disks, and gramophone needles to create the initial charge. The 'work' was done by an electric motor. Based on the length of spark it generated, I think it produced over 200,000V.

His dad took it work, where they designed telephones, and tested early electronic telephones with it.

1. The mechanism is electrostatic repulsion -- the Coulomb force. The battery forces extra electrons onto the negative plate of the capacitor. The excess charge pushes an equal number of electrons off of the other plate and into the rest of the circuit. To the rest of the circuit, it looks like there's a current through the capacitor, since electrons go into one end and come out the other.

2. If you replace the battery with a short circuit, the capacitor will indeed produce a discharge current in the opposite direction of the charging current. (It's sort of like a spring.) If you replace the battery with an open circuit, no current flows and the capacitor remains charged.