Series Circuits

What is a Series Circuit?

In a series circuit, components are connected end-to-end, forming a single path for current to flow. The same current flows through every component in the series chain.

Series Circuit Rules

• •Current is the same everywhere: I_total = I₁ = I₂ = I₃
• •Voltages add up: V_total = V₁ + V₂ + V₃
• •Resistances add up: R_total = R₁ + R₂ + R₃
• •If one component fails open, the entire circuit stops working (like old Christmas lights)

Voltage Drops in Series

Each resistor in a series circuit drops a portion of the total voltage, proportional to its resistance. The voltage drop across each resistor is found using Ohm's Law: V = I × R. The sum of all voltage drops equals the source voltage.

Real-World Series Circuits

Series circuits are found everywhere in electronics. Old-style Christmas lights were wired in series — if one bulb burned out, the entire string went dark. Battery cells inside a flashlight are stacked in series to increase voltage. Fuses and switches are always placed in series with the circuit they protect, because opening the series path stops all current.

Troubleshooting Series Circuits

Because there's only one current path, a break anywhere stops the entire circuit. To find a faulty component, measure the voltage across each one — the broken (open) component will have the full source voltage across it, while the rest show 0V.