Moving charge, resistance and the circuits built from them.
Current and current density, drift of free electrons, Ohm's law, resistivity and its temperature dependence, thermistors and superconductors, emf and internal resistance, Joule heating, Kirchhoff's laws, series and parallel resistors and cells, the Wheatstone bridge, ammeters, voltmeters, the potentiometer, charging and discharging capacitors, and atmospheric electricity.