Series and Parallel Circuits

Series Circuits: Single-Path Flow and Voltage Division

A series circuit provides only one continuous path for electric current to flow. Because there are no branching paths or detours, current is identical at every point in a series circuit. Whether you check the circuit right next to the power source or between two components, the exact same rate of electrical charge passes through each element. In a circuit diagram, an ammeter measures a component's current when connected in series with it, placing the meter directly in that single flow path.

Total resistance in a series circuit equals the sum of all individual resistances. Adding a resistor in series increases the total resistance of the circuit. When total resistance increases while source voltage remains constant, the overall current in the circuit decreases. This relationship is easy to visualize with lighting: with a constant supply voltage, adding identical bulbs in series reduces the current and usually makes each bulb dimmer.

In a simple series circuit, voltage drops across each load, while the current remains the same through every load. The sum of all voltage drops across components in a series circuit equals the source voltage. This matches Kirchhoff's Voltage Law, which states that the algebraic sum of voltage rises and drops around a closed loop is zero. In a series circuit, a resistor with higher resistance develops a larger voltage drop than a resistor with lower resistance, meaning the components divide the source voltage in proportion to their individual resistances.

Because a series circuit relies on a single unbroken line, its continuity is fragile. If any component in a series circuit fails open, current flow stops completely through the entire circuit. For instance, removing one light bulb from a simple series circuit breaks the continuous loop and causes all other bulbs in that circuit to go out.