Year 6 Science: A complete circuit
Part of the Year 6 Science cells, brightness and volume chapter. Chapter overview · whole chapter on one page
A complete circuit
A complete circuit is a loop. Electricity flows from the positive end of the cell, round the wires and through the bulb or the buzzer, and back to the negative end.
If the loop is broken, anywhere, the electricity cannot flow and the bulb or buzzer does not work. Each part of a circuit needs to be connected.
The table names the parts of a simple circuit, and what each one does.
| Part | What it does |
|---|---|
| cell | provides the energy; it has a positive and a negative end |
| wire | carries the current round the loop |
| bulb | lights up when current flows through it |
| buzzer | makes a sound when current flows through it |
Key ideas
- A complete circuit is a loop with no gaps.
- Electricity flows from the positive end of the cell, round the loop, and back to the negative end.
- A bulb or buzzer works only when it is part of a complete loop.
- More cells give more voltage, which makes a bulb brighter or a buzzer louder.
Method. Check the wires round the loop.
- Check the loop. The wires go all the way round, and the bulb is in the loop.all the way
- Decide. So the loop is complete, and the answer is yes.yes
- Write the answer. yes
Check. Every part is connected in the loop. ✓
Method. Think about the broken loop.
- Think about the gap. With a wire removed, the loop has a gap, so the electricity cannot flow.gap
- Decide. So the bulb does not light, and the answer is no.no
- Write the answer. no
Check. A gap in the loop stops the current. ✓
Method. Recall the name.
- Recall. A circuit joined all the way round is a complete circuit.complete circuit
- Check the meaning. Complete means there are no gaps in the loop.no gaps
- Write the answer. complete circuit
Check. Complete means there are no gaps. ✓
Watch out
Watch out: a bulb may not light because the loop is broken, not because the bulb is faulty. Check every connection first.
Exam tip
Exam tip. When a circuit does not work, say that the loop must be complete, and check each connection.
Try it (with your teacher, or a grown-up at home). With a teacher, build a loop with one cell, one bulb in a holder and two wires. Make the bulb light. Then remove one wire, and watch the bulb go out. Put the wire back. Never connect a wire directly across the two ends of one cell.
Exercise 9D A complete circuit
Method. Read the idea.
- Read the idea. Electricity must flow all the way round, so the loop must be complete.all the way round
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. A gap stops the current. ✓
Method. Read the table.
- Read the table. The cell gives the energy to the circuit.energy
- Write the word. So the part is the cell.cell
- Write the answer. cell
Check. The cell is the source of the voltage. ✓
Method. Read the table.
- Read the table. The bulb lights up when current flows through it.lights up
- Write the word. So the part is the bulb.bulb
- Write the answer. bulb
Check. A buzzer makes a sound instead. ✓
Method. Read the table.
- Read the table. The wire carries the current round the loop.carries
- Write the word. So the part is the wire.wire
- Write the answer. wire
Check. Wires must be joined without gaps. ✓
Method. Think about the loop.
- Think about the loop. A wire removed leaves a space in the loop.space
- Decide. So there is a gap, and the answer is yes.yes
- Write the answer. yes
Check. A gap breaks the circuit. ✓
Method. Think about the current.
- Think about the current. With a gap, the current cannot flow round the loop.cannot flow
- Decide. So the bulb does not light.no
- Write the answer. no
Check. Without current, the bulb is off. ✓
Method. Read the definition.
- Read the definition. A complete circuit is a loop with no gaps.no gaps
- Write the answer. complete circuit
Check. Complete means joined all the way round. ✓
Method. Read the key idea.
- Read the key idea. Electricity flows from the positive end of the cell, round the loop, and back to the negative end.from the positive
- Write the answer. positive
Check. It returns to the negative end. ✓
Method. Think about the gap.
- Think about the gap. A gap stops the current, however strong the cell is.stops the current
- Decide. So Priya is not right.no
- Write the answer. no
Check. The loop must be complete. ✓
Method. Multiply by 1.5 volts.
- Multiply. Two cells give 2 x 1.5 volts.2 x 1.5 = 3.0
- Write the answer. 3.0 volts
Check. The bulb is rated 4 with two cells. ✓
Method. Think about the current.
- Think about the loop. A complete loop lets the current flow round to the bulb and back.flow
- Think about the gap. A gap stops the current, so the bulb is off.stops
- Write the answer. Accept any sentence that says a complete loop lets the current flow through the bulb, but a gap stops the current.
Check. A complete loop is needed for current. ✓
Method. Think about the cell.
- Think about the short circuit. The wire takes the current straight across the cell, with no bulb.straight across
- Think about the danger. This makes the cell and wire hot, so it is dangerous.hot
- Write the answer. Accept any sentence that says it makes a short circuit, which makes the cell and wires hot, and the cell can be damaged.
Check. Never connect a wire straight across a cell. ✓
Method. Compare the two circuits.
- Think about the complete loop. The two cells drive current round the complete loop.drive current
- Think about the gap. With a gap, the two cells cannot drive any current round.cannot drive
- Write the answer. Accept any sentence that says the complete loop lets the higher voltage drive the current round, while a gap stops it entirely.
Check. A complete loop is needed for voltage to work. ✓