Insulators have valence shells that are more than half full of electrons and, as such, are tightly bound to the nucleus and difficult to move from one atom to another.

Most households use electricity with a voltage of 110V.

Connecting the 4 batteries in series multiplies their voltage while keeping their current the same yielding a 36V 10A configuration. Connecting the 4 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 9V 40A configuration. Using a series-parallel connection, 2 batteries can be connected in series and 2 can be connected in parallel resulting in a 18V 20A configuration.

Capacitors store voltage and are used in circuits as temporary batteries. Capacitors are charged by DC current (AC current passes through a capacitor) and that stored charge can later be dissipated into the circuit as needed. Capacitors are often used to maintain power within a system when it is disconnected from its primary power source or to smooth out or filter voltage within a circuit.

Current in an electric circuit creates heat when the current overcomes resistance in the wire.