What Are Series and Parallel Connections?
In a series connection, components sit end to end: the same current flows through all of them, the voltage divides among them, and resistances add up. In a parallel connection, components share the same two nodes: the voltage is common, the current splits between branches, and the total resistance drops below even the smallest resistor. The choice depends on whether you want a shared current or a shared voltage.
There are two basic ways to connect components in a circuit: series and parallel. Which one you choose determines how the current, voltage and total resistance behave.
What Is a Series Connection?
Components are connected end to end, forming a single path. In a series connection:
- The current is the same in every component.
- The voltage is divided among the components.
- The total resistance is the sum of the resistances: R = R₁ + R₂ + …
Example: 100 Ω and 200 Ω in series give an equivalent resistance of 300 Ω.
What Is a Parallel Connection?
Components are connected side by side between the same two nodes. In a parallel connection:
- The voltage is the same across every component.
- The current is divided among the branches.
- The total resistance is found with: 1/R = 1/R₁ + 1/R₂ + …
Example: two 100 Ω in parallel give an equivalent resistance of 50 Ω (for equal resistors: one resistor ÷ count).
| Series | Parallel | |
|---|---|---|
| Current | Same | Divided |
| Voltage | Divided | Same |
| Total resistance | Rises (sum) | Falls |
Series and Parallel in Batteries
The same logic applies to power sources: connect batteries in series and the voltage adds up (two 1.5 V → 3 V); connect them in parallel and the voltage stays the same but the capacity (runtime) increases.
Where Is It Used?
Series connection is used in LED strings and voltage division; parallel connection is used to power multiple loads that share the same voltage. At the base of the calculations is always Ohm's law.
For the mathematical basis of these rules: What Is Ohm's Law?
Frequently Asked Questions
How do current and voltage behave in a series circuit?+
What changes in a parallel circuit?+
Should batteries be wired in series or parallel?+
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