By David Dunning – Updated March 24, 2022
Electricity is the result of electrons moving from one atom to another. In a series circuit, electrons have only one path. Any break along this path interrupts the flow to the entire circuit. In a parallel circuit, there are multiple branches, giving electrons separate pathways. A fault in one branch leaves the others unaffected.
In a series circuit, the current is governed by Ohm’s Law, I = V / R, where I is current, V the supplied voltage, and R the total resistance. Because the same electrons travel through every component, the current is identical at every point in the circuit.
In a parallel circuit, each branch has its own resistance. The current through a branch is inversely proportional to its resistance (I₁ = V / R₁, I₂ = V / R₂, etc.), and the total current supplied by the source equals the sum of all branch currents.
Series circuits exhibit a voltage drop across each component. The drop is proportional to its resistance, and the sum of all drops equals the source voltage.
Parallel circuits present the same voltage across each component because all branches are connected between the same two nodes. Thus, every element experiences the full source voltage.
In series, the overall resistance is simply the sum of individual resistances: R_total = R₁ + R₂ + … + Rₙ.
In parallel, the overall resistance is always lower than the smallest individual resistance. It is calculated with the reciprocal formula: 1 / R_total = 1 / R₁ + 1 / R₂ + … + 1 / Rₙ.
Both configurations are foundational for connecting components such as resistors, diodes, switches, and more. They enable designers to control current paths and voltage levels to achieve desired circuit behavior.
While series circuits enforce equal current through all components, parallel circuits enforce equal voltage across each component. Understanding these distinctions is crucial for effective circuit design.
— Source: David Dunning, Updated March 24, 2022
