27.12 - Circuits with series and parallel wiring
Circuits commonly include some components that are wired in series and some that are
wired in parallel. The diagrams to the right show an example of such a circuit.
You can use the current to determine what is in series and what is in parallel. If the
current flows along a single path from one component to another, then the two
components are in series. If the current divides, then the components are in parallel.
In the circuit on the right, for example, the two resistors on the far right wire of the
circuit, labeled R 2 and R 3 , are in series with one another. There is no junction between
them, no place for the current to split. Since there is only a single path for the current
between the resistors, the resistors are in series, as emphasized in Concept 2.
This pair of series resistors is wired in parallel with the resistor in the middle, R 1. Both
branches are in parallel with the battery. Consider current that exits the battery. It
encounters a junction at A where it can flow to R 1 or to the R 2 R 3 combination. The
current then recombines at B after flowing through those resistors. The same potential
difference exists across R 1 as across the R 2 R 3 combination. This means R 1 is in
parallel with the R 2 R 3 combination.
Mixed circuits
A circuit can be part series, part parallel
Components in series
No junction separates series
components
(Single current path between them)Part of circuit is parallel
Junctions separate parallel components
(Current differs, potential difference the
same)27.13 - Sample problem: circuits with series and parallel wiring
The diagram shows a circuit with three resistors and asks which resistors are wired in series and which are wired in parallel.
What is the strategy?
- Use the definitions of series and parallel wiring.
- Once two or more resistors are identified as series or parallel, simplify the circuit by determining the equivalent resistance. Then see