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.

The joule is a unit of measurement for energy.

Direct current flows in only one direction in a circuit, from the negative terminal of the voltage source to the positive. A common source of direct current (DC) is a battery.

Inductance is a property of an AC circuit (or a component in an AC circuit) that quantifies resistance to changes in current. The current in an AC circuit is continuously changing and inductive reactance (the opposition to change) depends both on the inductance of the circuit or component and the rate at which the current is changing.

A moving electric current produces a magnetic field proportional to the amount of current flow. This magnetic field can be made stronger by winding the wire into a coil and further enhanced if done around an iron containing (ferrous) core.