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Physics · Key Stage 2 · The School
The loop must be closed
A circuit needs an unbroken loop from one end of the cell, through the components, and back to the other end. Break it anywhere and everything stops — which is all a SWITCH is: a deliberate gap you can close. If a bulb does not light, look for the break before you blame the bulb.
The parts and their symbols
CELL (one) or BATTERY (two or more) supplies the push. WIRES carry it. A BULB gives light, a BUZZER sound, a MOTOR movement. Scientists draw circuits with SYMBOLS rather than pictures, because a symbol diagram is unambiguous and anyone in the world can read it.
What lets it through
Metals CONDUCT — the wires are metal for that reason. Plastic, wood, rubber and glass are INSULATORS. Test objects by putting them into a gap in your circuit and seeing if the bulb lights. That is also why wires are metal inside and plastic outside: one to carry it, one to keep it in.
The bulb will not light. Do not swap the bulb first — test the loop in order. Are both crocodile clips gripping bare metal, not plastic coating? Is the cell the right way round and not flat? Is the bulb screwed fully into its holder? Is the switch closed? Change ONE thing and retest each time. Nine times out of ten it is a loose clip or a flat cell, and swapping components at random hides which it was.