This section describes circuits - electric "machines".
A circuit is a loop of wire with
its ends connected to an energy source such as a cell* or a battery*.
One end of the wire is connected to
the positive terminal; the other end
of the wire is connected to the negative terminal.
The wire is connected in this way so a current* can flow through it.
Having connected our circuit, we can use it to light an electric lamp,
to run an electric motor, to heat an electric element* and so on.