A flashlight has a battery, a bulb, a switch and metal strips joining them. Together they make a circuit.
Key idea
Electricity flows only around a complete loop, a closed circuit: out of one end of the battery, through the wires and the bulb, and back into the other end. If the loop has a gap, it is an open circuit and the bulb stays dark.
A switch is a little bridge in the loop. Turned on, it closes the gap. Turned off, it opens the gap and the current stops.
Why it works
The battery pushes electric charges around the loop like a pump pushing water around a ring of pipes. A break anywhere stops the whole flow.
Worked example: Will it light?
A wire goes from the top of a battery to a bulb, but no wire goes from the bulb back to the battery. Does the bulb light?
- The current needs a path out and a path back.
- There is no path back, so the loop is open.
Answer: No, the bulb stays dark.
Common mistake
Thinking one wire is enough because "the electricity goes to the bulb". It must go through the bulb and back.
Try it at home
- With a grown-up, open a flashlight and take out the batteries.
- Look for the metal spring and strips that touch each end of the batteries, the switch and the bulb. Trace the loop with your finger.
- Never take apart anything that plugs into the wall, and never put anything into an outlet.
Going further. Build circuits safely on screen in the Circuit Builder. Later: Circuits in Physical Science.