Before we leap into the fray, let’s first perform a couple of simple thought experiments involving switches and light bulbs. Consider an electrical circuit consisting of a power supply, a light, and two switches connected in series, one after the other [Figure. 5.1(a)].
The switches are the inputs to the circuit and the light is the output. A truth table provides a convenient way to represent the operation of the circuit [Figure. 5.1(b)]. As the light is only on when both the a and b switches are