Topics · Primary Science · Systems: Electrical Circuits
Electrical circuits: series and parallel
Electricity needs a complete loop. Whether the parts sit in one loop or in separate branches decides what happens when a bulb is removed — and that is the question papers ask most.
- 236 exam papers analysed
- appears in 88% of P6 Science papers
- ~3 min read
01 A circuit must be complete
Electricity flows only round an unbroken loop from one end of the battery to the other. Break the loop anywhere and everything stops.
A switch works by deliberately breaking it. Open the switch, the loop is broken, the bulbs go out.
A circuit needs a source (battery), something using the electricity (bulb, buzzer, motor), and conductors joining them — wires, usually copper inside plastic.
02 Series and parallel
Series — one single loop. The electricity has no choice of route, so it passes through every part in turn.
Parallel — the loop splits into branches, and each branch is its own path back to the battery.
The difference matters for one reason above all: what happens when one bulb is removed.
03 Remove one bulb
This is the standard question, and both halves need the reason, not just the outcome.
- Series — remove one bulb and the others go out. The single loop is broken, so nothing flows anywhere.
- Parallel — remove one bulb and the others stay lit. Each branch is its own complete loop, so the remaining ones are untouched.
- Series — more bulbs makes each one dimmer, because they share what the battery provides.
- Parallel — more bulbs stay equally bright, but the battery runs down faster.
- Say why, not just what. “The circuit is broken” or “each branch is a complete path” is where the mark sits.
04 Conductors, insulators and safety
A conductor lets electricity through: metals, and copper above all. An insulator does not: plastic, rubber, wood, glass.
That is why a wire is copper inside plastic — the metal carries the electricity, the plastic keeps it from reaching you.
In the standard test, a material is placed in a gap in the circuit. Bulb lights → conductor. Bulb stays dark → insulator. Which is also how a question can hide a broken wire: everything looks connected but the bulb is dark.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- circuitsaySUR-kitmore than onecircuits
A complete loop that electricity can flow round.
- seriessaySEER-eez
Parts joined one after another in a single loop.
- parallelsayPA-ruh-lel
Parts on separate branches, each its own path back to the battery.
- conductorsaykuhn-DUK-tuhmore than oneconductors
A material that lets electricity through. Metals, especially copper.
- insulatorsayIN-syuh-lay-tuhmore than oneinsulators
A material that does not let electricity through: plastic, rubber, wood.
- switchmore than oneswitches
A part that breaks or completes the circuit on purpose.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P5
Complete circuits, conductors and insulators, and drawing simple circuits.
Practise P5 Systems: Electrical Circuits — 10 questions →60% of P5 papers
- P6
Series and parallel, what happens when a bulb is removed, and faults in a circuit.
Practise P6 Systems: Electrical Circuits — 10 questions →88% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“Take out one bulb and the rest always go out.”
Only in series. In parallel each branch is its own loop, so the others stay lit.
“The circuit was complete but the bulb did not light, so the bulb is fine.”
Check for a break anywhere — a loose wire, an open switch, or an insulator in the gap.
“All metals conduct, so all metals are magnetic.”
Two different properties. Copper conducts electricity well and is not magnetic at all.
“More bulbs in parallel makes them dimmer.”
They stay equally bright. It is series where bulbs share and dim.
“The plastic on a wire is just to hold it together.”
It is an insulator, keeping the electricity in the wire and away from you.
Now try it
20 questions across 2 levels, marked as you go with the working shown.