Series and parallel circuits — Engineering, 14–17 years
The arrangement of components changes how current has paths through a circuit, which affects brightness, reliability and control.
One path or several
In a series circuit, components share one continuous path, so a break stops the whole circuit. In a parallel circuit, branches give current more than one path, so one branch can stop while the others keep working.
The problem of one failure
Early strings of lamps could all go dark when one bulb failed. Engineers needed circuits that matched the job: a series path can simplify a chain, but parallel branches keep separate devices operating and make faults easier to isolate.
Two lamps in two arrangements
Connect two identical lamps to a battery in series: there is one loop, and both lamps go out if either is removed. Connect them in parallel: there are two branches, so removing one leaves the other lit. The arrangement changes the behaviour, not the lamp itself.
Parallel does not mean brighter by magic
It is tempting to think that adding a parallel branch always makes every lamp brighter. The battery and wiring also matter: extra branches can draw more current, and a weak source may make the voltage fall or run down faster.
Why homes use parallel circuits
Household lights and sockets are generally arranged in parallel, so switching off one lamp does not switch off every other one. Each device can receive the supply independently, while protective devices can disconnect a faulty branch.
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