Resistors are used to limit voltage and/or current in a circuit and can have a fixed or variable resistance.  Variable resistors (often called potentiometers or rheostats) are used when dynamic control over the voltage/current in a circuit is needed, for example, in a light dimmer or volume control.

Connecting the 10 batteries in series multiplies their voltage while keeping their current the same yielding a 120V 20A configuration. Connecting the 10 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 12V 200A configuration. Using a series-parallel connection, 5 batteries can be connected in series and 5 can be connected in parallel resulting in a 60V 100A configuration.

Connecting the 8 batteries in series multiplies their voltage while keeping their current the same yielding a 96V 25A configuration. Connecting the 8 batteries in parallel multiplies their current while keeping their voltage the same yielding a 12V 200A configuration. Using a series-parallel connection, 4 batteries can be connected in series and 4 can be connected in parallel resulting in a 48V 100A configuration.

A photovoltaic cell (also known as a solar cell) converts energy from the sun into electrical energy.

Electricity is delivered from power stations to customers as AC because it provides a more efficient way to transport electricity over long distances. A line drop is a decrease in voltage between two points on an electrical transmission line due to resistance in the line. A lower current and higher voltage across the line will help compensate for the line drop.