Practical takeaway
Series parts share one current path. Parallel branches share the same two connection points. That difference changes how voltage, current and resistance behave.
Electricity & Electronics
Series & Parallel Circuits
Use two resistors to see how series and parallel connections change total resistance, then move into a complete circuit to see what happens to voltage and current.
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Technician exam focus
Recognize series and parallel connections and calculate simple equivalent resistance relationships expected at Technician level.
Two common connections
Series resistors
In this lesson we are using resistors as the example. In series, the resistors are connected one after another in a single current path. Their resistance values add.
Parallel resistors
In parallel, both resistors connect across the same two circuit points, creating separate branches. The equivalent resistance is lower than either resistor by itself.
The idea applies beyond resistors
Other electrical components can also be connected in series or parallel. We start with resistors because their voltage, current and resistance relationships are easy to calculate and see.
Series
Parallel
These drawings use three resistors to make the pattern easier to see. A series or parallel circuit can have more or fewer than three components.
STEMulation
Combine two resistors
This calculator uses two resistors so the arithmetic stays easy to follow. Choose series or parallel, then change R1 and R2. Real circuits can use more than two.
Next: use it in a complete circuit
Ohm’s Law in Series & Parallel Circuits
See source voltage, current, individual resistor voltage, a working switch, and a snap-together circuit builder.