The loop has to be unbroken
One wire joins a cell to a lamp. Nothing happens. A second wire, and the lamp glows.
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The idea
Step 1 of 3
- One wire from the cell to the lamp. There is a gap. The lamp is dark.
- A second wire joins the lamp back to the cell. The loop is closed.
- Trace the path all the way round. This whole path is the circuit.
- A cell has two ends called terminals. One is positive (+). One is negative (−).
- A lamp has a thin wire inside, the filament. It glows when electric current, the flow of electricity, passes through it.
The rule
The lamp glows only when the path is closed, with no gap. Because current needs a full path, a gap stops the lamp.
A lamp with a filament has no right way round. Either end can join the + terminal.