lesson
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If a single bulb burns out in an old string of holiday lights, every single bulb goes dark instantly.
That happens because the bulbs form a series circuit β a single, unbroken pathway where electric charge must pass through every component one after the other.
How do electric current, voltage, and resistance behave when everything is lined up in a single line?
What Is a Series Circuit?
In a series circuit, all electrical components are connected end-to-end to form one continuous loop from the power source and back.
πInteractive/animated diagram of a series circuit. A rectangular circuit with a 12V DC battery at the left, an open/closed toggle switch at the top, a resistor labeled R1 on the right, and a light bulb labeled R2 at the bottom. Yellow glowing dots represent electrons moving steadily counter-clockwise along the wire when the switch is closed. Three ammeters placed at different points all display '2.0 A' in bright blue digital readouts. Clean modern design with light background (#f8fafc), dark circuit lines (#1e293b), rounded components, and a subtle glowing current effect.
Because there are no branches or forks in the road, what happens to the electric current as it travels through the loop?
Rule 1: Current Is the Same Everywhere
An electric current (symbol I) is the rate of flow of electric charge around a circuit, measured in amperes (extA).
In 1845, German physicist Gustav Kirchhoff formalized the principle of conservation of charge, proving that electric charge cannot pile up or vanish inside a wire.
Because there is only one pathway, the number of coulombs passing any point per second is identical throughout the entire circuit.
Itotalβ=I1β=I2β=I3β=β¦
πA visual explanation of constant current in a series loop. Shows a single water pipe loop with a pump and two water wheels representing resistors. Flow rate meters installed before Wheel 1, between Wheel 1 and Wheel 2, and after Wheel 2 all display '2.0 L/s' (or Amps). Text annotations explain: 'No junctions = no splitting. Charge in = Charge out.' Visual color coding in teal (#0ea5e9) and deep slate (#1e293b).