Experiments you can run yourself.
Coulomb's law: why like charges repel and unlike charges attract, and how the force falls with the square of the distance. Interactive simulation.
The field strength of a point charge E=kQ/r² is greatest close to the charge (∝1/r²). Field lines run from + to −, their density shows the field strength, and they never cross.
The capacitance of a parallel-plate capacitor C=ε₀·S/d grows as the plate separation decreases. The charge is Q=CU, and the stored energy is E=½CU².
V=kQ/r; the work depends on the potential difference, not on the path.
In parallel the capacitances add; in series — the reciprocals.
Measuring the charge of an oil drop: always a multiple of e — the 1923 Nobel Prize.