For whatever reason, there are nine light bulbs installed in our living room ceiling (three recessed, controlled by two different switches, and six on a zigzag-shaped fixture, controlled by a single switch). I clearly think this is an excessive number, as evidenced by the fact that, a few weeks ago, I was working away happily in what I felt was a perfectly adequately lit room. The SigFig then walked in, looked up, and pointed out that most of the bulbs in the fixture had burned out. A single light bulb soldiered on amongst its burned-out brethren.
I did what any scientifically-minded person would: I started thinking about circuits.
Anything that runs on electricity contains some form of circuit. Simple circuits consist of electrical energy sources (such as batteries or home electric grids), resistors that transform that electrical energy into other forms of energy (such as heat and light), and wires to connect these elements. Circuit diagrams show how the parts of the circuit are put together.