A circuit needs a complete path — Engineering, 7–10
See how a battery, wires, switch and lamp work together only when electricity has a complete route to follow.
A loop for electricity
A circuit is a complete loop that lets electric current travel from one side of a battery, through parts such as a lamp, and back to the other side. A switch opens or closes the loop. The lamp lights only when the path is closed and the parts are connected properly.
Why must the path close?
People wanted useful light and movement without burning a fuel beside every object. Engineers needed a safe way to carry electrical energy from a source to a device and back again. The complete loop solves that problem, while a gap stops the current instead of letting it jump across.
Making one lamp light
Take one 1.5-volt battery, two wires and a small lamp. Touch one wire from the battery’s raised end to the lamp’s metal tip, then touch the second wire from the lamp’s metal side to the battery’s flat end. The loop is now complete, so the lamp lights; remove one wire and it goes out.
The common mix-up
A common thought is that touching one wire to a battery and the lamp is enough, because electricity is invisible and the lamp is nearby. But current needs a route all the way around the circuit. Also, never test circuits with wall sockets or mains electricity; use only safe classroom batteries and follow an adult’s instructions.
Circuits in daily life
Torches, doorbells, bicycle lights and toys all use circuits. Pressing a torch button closes a path, while releasing it opens the path to save the battery. Larger systems contain many circuits with safety parts that switch off when too much current flows.
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