1Two things electricity needs
It has to make a full loop — and a bulb only glows when the flow goes through it
Electricity is like a one-way parade that leaves the battery, marches through the wire, and must get all the way back. No complete loop, no march. And a bulb only lights up while the parade is actually flowing through that bulb.
The loop must close
The flow only moves if the path is unbroken — out from the battery and back. Leave a gap and the whole parade stops.
Flow makes it glow
A bulb shines only while the flow passes through it. Cut off its flow and the light goes dark.
2Two ways to wire the same bulbs
One big circle, or lots of little loops
The "everyone holds hands" string
All the bulbs sit on one shared path, like kids in a circle holding hands. The flow has to go through every single bulb, one after another, to finish the loop.
The "everyone has their own door" string
Each bulb gets its own little loop straight back to the battery. The flow splits up and visits the bulbs side by side, not one-after-another.
3Your turn — turn on the power
Push the battery and watch the flow light the bulbs
Here's a single-loop string. Slide the battery up and watch the power flow around the loop and light every bulb. This is just to feel how the loop works — the real test comes next.
4Now break one bulb — on purpose
Same bulbs. Two wirings. One gets unscrewed.
Here are two strings made of the exact same bulbs — one wired as a single loop, one wired side by side. You're about to unscrew one bulb in each of them.
Guess before you find out
You unscrew one bulb in each string. In which string do the other bulbs stay lit?