When you flip a switch in your house to turn on a light, have you ever thought about what is really happening? You are closing a circuit that runs from the light bulb, through the wires the run through your walls to the light switch, to the wires that go to the circuit breaker in your house, and all the way through the power lines to the power plant miles from your house. At this power plant, some sort of fuel is being converted into electrical energy. The fuels source may be renewable, like solar or wind, or it may be a fossil fuel, like coal or natural gas, or it may even be nuclear. Each of these source has its downsides, so we should make every effort to reduce the amount of electricity we use.