The capacitor is the device that makes the idea of storing electrostatic energy concrete. Two simple facing plates, one charged and the other , create a uniform field in the space between them, in which the accumulated energy resides. From here a chain of consequences follows: the definition of capacitance, the role of insulating materials (dielectrics) that enhance it, and the discovery that the energy is not on the charges but in the field between them.
This section gathers three atoms that follow this thread: from the essential geometry of the parallel-plate capacitor, to the microscopic physics of polarisation, up to the — apparently paradoxical — behaviour of the energy when a dielectric is inserted with the battery connected or disconnected.
- Parallel-plate capacitor — facing plates, capacitance , energy stored in the field.
- Dielectrics and polarisation — how an insulator polarises and multiplies the capacitance by .
- Energy and dielectric: battery connected or disconnected — why the same mica makes the energy fall or rise depending on the experiment.