- Circuit Diagrams -

Circuits are collections of electronic components connected with wires. Meaningful use of electricity and electronics requires a working knowledge of individual electronic components as-well-as an understanding of ways they work together in circuits. Bulbs, resistors, rectifiers, transformers, and capacitors are examples of electronic components.

Circuits are powered by batteries (or some other voltage source) which drive current through the components. The ideas of voltage and current are essential to an understanding of electricity. Voltage and current measurements are a regular part of circuit analysis and design. Voltmeters measure voltages (in volts) and Ammeters measure current (in amps).

Real circuits are usually represented on paper as circuit diagrams. These electronic "blueprints" are used around the world for designing, understanding, and documenting real circuits. Circuits are pictured in a variety of ways, with photographs, sketches, and diagrams. Each kind of picture is a different level of abstraction, and each is useful in its own way.

This example starts with photographs showing a circuit with just a two light bulbs powered with a 9 volt battery. One photo shows wires connected by twisting them together , the next photo shows wires connected with a solderless bread board. Both ways of connecting make the same circuit.

Figure P1a
Bulbs and wires

This photograph has a lot of information in it. It shows how the wires loop around, the shape of the bulbs, the type of socket used for the bulbs, and even the kind of 9 volt battery.

Figure P1b
Bulbs and breadboard

This photograph show how wires can be connected in a solderless breadboard. This picture also has a lot of information which is unimportant to the ideas of this circuit.

Figure P2
Circuit sketch

Sketches have less information that photographs. They present only the important features of the circuit. This sketch is a little fancier than necessary, showing the style of the bulb sockets and picturing green wire.

Figure P3
Circuit diagram

A circuit diagram has much less information than a photograph. It uses symbols to represent the electronic components and straight lines to prepresent the connections. The circuit diagram is an abstraction of the real circuit, and contains only the essential information about the components and their connections. Another example is a circuit with two bulbs connected in parallel. Parallel circuits have branch points where currents split other branch points where currents rejoin.

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