In the circuit in Figure 4 the switch is represented by a pushbutton. Pushing the button once closes the circuit. Pushing it again opens the circuit. Click on the pushbutton to make it change state. In many cases, we can abstract a circuit still further.
Every electric circuit requires a connection to a power source and a return to the power source.
Since we know these elements must be present, we can omit them from the diagram. All that's left in the picture is the pushbutton and the LED, as shown in Figure 5. The reduction in size of the diagram will be an advantage as we build more complex circuits. Digital Works omits the power source and return wires as we have done here. In the next section we will see that transistors can function as switches and can be wired in series or parallel to compute Boolean functions.