Primary 6 · Science · Physical sciences
Electric circuits
Students learn that electricity flows only around a complete circuit, identify conductors and insulators, and draw simple circuit diagrams.
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These lessons were written around Australian Curriculum strands and matched to Singapore levels by age (Primary 1 is the first year of primary school). They are not aligned to MOE syllabuses or the PSLE, so check them against the syllabus your child is working towards.
Learning goals
Learners will
- Explain that electricity flows only when there is a complete circuit.
- Test and classify materials as electrical conductors or insulators.
- Draw simple circuits using standard circuit symbols.
Success looks like
- I can build a circuit that lights a bulb and explain why it works.
- I can test objects and sort them into conductors and insulators.
- I can draw a circuit diagram with a cell, a switch, a lamp and wires.
The big idea
Electricity can flow only around a complete circuit: an unbroken loop that goes from one end of the battery, through the wires and the bulb, and back to the other end of the battery. If there is a gap anywhere in the loop, the electricity stops and the bulb goes out.
A circuit with no gaps is a closed circuit and works. A circuit with a gap is an open circuit and does not work. A switch is simply a safe way of making and breaking a gap. When the switch is closed (on), the loop is complete. When it is open (off), there is a gap.
The cell (battery) provides the push that makes electricity flow. The electricity carries energy from the cell to the bulb, where it is changed into light and heat. The electricity is not used up: the same amount flows all the way round the loop and back to the cell.
Some materials let electricity flow through them easily. These are conductors. All metals are conductors, such as copper, aluminium, steel and iron. The 'lead' in a pencil is made of graphite, which conducts a little too.
Other materials block electricity. These are insulators, such as plastic, rubber, wood, glass, paper and fabric. Electrical wires have copper inside to carry the electricity and a plastic coating outside to keep the electricity in and protect our hands.
Scientists and electricians draw circuits using circuit diagrams. Each part has a simple symbol:
- Cell: a long thin line and a short thick line side by side. The long line is the positive (+) end.
- Lamp (bulb): a circle with a cross inside it.
- Switch: a break in the wire with a short line that looks like a gate. Open means off; closed means on.
- Wire: a straight line. Draw wires with a ruler and make corners square, so the diagram is neat and easy to follow.
Safety: only ever experiment with small batteries such as AA or AAA cells. Never use power points or mains electricity, which can kill. Never join a wire straight from one end of a battery to the other with nothing else in the circuit: this is a short circuit, and the wire and battery can get hot. Keep button batteries away from young children, as they are very dangerous if swallowed.
Worked examples
Will the bulb light?
Sam clips both wires from the bulb to the same end (+) of the battery holder. Will the bulb light?
- Trace the path with your finger: from the + end of the battery, along a wire to the bulb, along the other wire… back to the + end.
- The path never reaches the other (−) end of the battery, so the loop is not complete.
- Move one wire to the − end. Now the path goes from + through the bulb to −, making a complete circuit.
Answer: No. The bulb lights only when one wire goes to the + end and the other to the − end, making a complete loop.
Testing conductors and insulators
Use a circuit with a gap to test a paperclip, a plastic ruler, foil and a wooden peg.
- Build a working circuit with the battery, the bulb and three wires. Unclip two wire ends to leave a gap.
- Touch both loose clips to the object being tested so the object fills the gap.
- If the bulb lights, the object conducts electricity. If it stays off, the object is an insulator.
- Record results in a table: paperclip (lights), foil (lights), plastic ruler (off), wooden peg (off).
Answer: Conductors: paperclip and foil (both metal). Insulators: plastic ruler and wooden peg.
Draw a circuit diagram
Draw a circuit diagram for a torch: one cell, one switch and one lamp joined in a loop.
- Use a ruler to draw a rectangle for the wire loop.
- On the left side, draw the cell symbol: a long thin line next to a short thick line.
- On the top side, draw the switch symbol: a gap with a short angled line like a gate.
- On the right side, draw the lamp symbol: a circle with a cross inside.
- Check the loop: can you trace from the cell, through the switch and lamp, and back to the cell without lifting your pencil? If the switch is closed, yes.
Answer: A neat rectangle with the cell, switch and lamp symbols each on one side, connected in a single loop.
Practice check
Have a go, then check your answers. Each answer comes with an explanation.
Answer guide for parents
What is needed for a bulb in a circuit to light?
A complete, unbroken loop from the battery, through the bulb and back to the battery — Electricity flows only around a complete circuit.
Which of these is a conductor?
A steel paperclip — Steel is a metal, and metals conduct electricity.
Why are electrical wires coated in plastic?
Plastic is an insulator, so it keeps electricity in the wire and protects us — Plastic does not conduct electricity, so it stops the electricity escaping into our hands or other wires.
In a circuit, the switch is open. What happens to the bulb?
It goes off because there is a gap in the circuit — An open switch makes a gap, so the circuit is broken and no electricity flows.
In a circuit diagram, what does a circle with a cross inside it stand for?
A lamp (bulb) — A circle with a cross is the symbol for a lamp.
A material that does not let electricity flow through it easily is called an ________.
insulator — Plastic, rubber, wood and glass are insulators.
When a switch is open, is the circuit complete or broken?
broken — An open switch leaves a gap, so the circuit is broken (open).
Which metal is found inside most electrical wires?
copper — Copper is an excellent conductor and bends easily, so it is used in most wires.
Watch out for
- Many students think one wire from the battery to the bulb is enough. Electricity needs a complete loop that goes out of one end of the battery and back into the other.
- Some think the bulb 'uses up' electricity so less flows back to the battery. The same amount of electricity flows all the way round; what the bulb uses is energy, which it gives out as light and heat.
- Students may think that because battery experiments are safe, all electricity is safe to play with. Mains electricity from power points is very dangerous and must never be used for experiments.
Tips for parents
- Beginner circuit kits with battery holders, bulb holders and alligator-clip wires make this lesson much easier than taping bare wires to batteries.
- Ask your child to predict before each test ('Will it light?') and then explain the result using the words 'complete circuit', 'conductor' or 'insulator'.
- Safety: an adult should supervise. Use only AA or AAA batteries, never power points. Disconnect the circuit if any part gets warm, never connect a wire directly across a battery, and keep button batteries well away from young children.
Go further
- Make a homemade switch from two drawing pins pushed into cardboard and a paperclip that can swing across to touch both pins. Adult help is needed with the drawing pins.
- Make a steady-hand game: bend a coat-hanger wire into a wiggly path and connect it into a circuit with a bulb or buzzer, so the light comes on when a wire loop touches the path. An adult should cut and bend the coat hanger.
- Draw a circuit diagram of a torch at home after examining how its switch, batteries and bulb connect (do not take apart anything that plugs into the wall).
About 50 minutes
You'll need
- Two AA batteries (1.5 volt cells) in a battery holder
- A small torch bulb (about 2.5 volts) in a bulb holder
- Three insulated wires with alligator clips at each end
- Items to test: a steel paperclip, aluminium foil, a coin, a plastic ruler, a rubber band, a wooden peg, a pencil, paper, a drinking glass
- Optional: a simple switch, or two drawing pins and a paperclip pushed into a piece of thick cardboard to make one
- Ruler and pencil for drawing diagrams
Key words
- circuit
- A complete, unbroken loop that electricity can flow around.
- cell
- A single battery, such as an AA battery, that pushes electricity around a circuit. Two or more cells joined together make a battery.
- conductor
- A material that lets electricity flow through it easily, such as copper or other metals.
- insulator
- A material that does not let electricity flow through it easily, such as plastic, rubber, wood or glass.
- switch
- A device that opens or closes a gap in a circuit to turn it off or on.
- circuit diagram
- A drawing of a circuit using simple standard symbols instead of pictures.
Still tricky?
For parents
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