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When a bulb will not light, pupils say it is broken or the battery is flat. This lesson gives them a route they can walk themselves: battery, wires, bulb contacts, switch, then the line between a conductor and an insulator.
Objectives — By the end the pupil can: (1) state that a bulb lights only when there is a complete loop from the battery positive terminal through the bulb and back to the negative terminal, and use that to explain why a switch sits inside the loop; (2) sort materials with a tester and say that copper, iron and salt water conduct while rubber, plastic and glass do not, and explain why wires are coated; (3) compare series and parallel: two bulbs in series share the voltage and are dimmer, and removing one puts both out, while in parallel each gets the full voltage, is brighter, and the other stays lit.
01 Prerequisites (3-minute check)
If any of these fails, fix it before the lesson starts.
| Skill | Quick check | Pass mark |
|---|---|---|
| Battery terminals | How many terminals has a battery and how do you tell them apart? | Two, marked positive and negative |
| Bulb contacts | How many contacts are at the base of a bulb? | Two, and both must touch |
| Open and closed | When a switch is closed, is the circuit complete or broken? | Complete, a closed circuit |
02 Lesson flow (45 minutes)
| Time | Stage | Tutor does | Student does |
|---|---|---|---|
| 0-5 min | Diagnose | Hand out a circuit that will not light and ask why | Say the first cause that comes to mind |
| 5-13 min | Show the loop | Light a bulb with one cell and two wires, then disconnect one wire | Point to where the break is |
| 13-23 min | Three acts | Teach the loop, conductors and insulators, then series and parallel | Repeat both terminals must return to the battery |
| 23-31 min | Test materials | Hand out a tester and eight items; predict before testing | Fill in prediction and result |
| 31-39 min | Compare bulbs | Wire two bulbs in series then in parallel and compare brightness | Say which is brighter and what removing one does |
| 39-45 min | Exit check | Collect three answers and mark at once | Name which step went wrong |
03 Teaching script (read it out)
Scene 1: Closed loop: leave the positive, return to the negative
Build the simplest circuit: one cell, two wires, one bulb. Once it lights, have the pupil trace the path with a finger, from the positive terminal, along the wire, into one contact at the bulb base, through the filament, out of the other contact, along the wire, back to the negative terminal.
Then disconnect one wire and the bulb goes out at once. That single action is the heart of the unit: the electricity was not used up, the path was broken.
Show the switch as what it really is, a piece of wire you can break and remake on demand. Closed means complete, open means broken.
Finish with a four-step check for a bulb that will not light: the cell has power and faces the right way; both wires are clamped at both ends; both contacts at the bulb base touch; the switch is closed. Use this order every time instead of swapping the battery first.
Then disconnect one wire and the bulb goes out at once. That single action is the heart of the unit: the electricity was not used up, the path was broken.
Show the switch as what it really is, a piece of wire you can break and remake on demand. Closed means complete, open means broken.
Finish with a four-step check for a bulb that will not light: the cell has power and faces the right way; both wires are clamped at both ends; both contacts at the bulb base touch; the switch is closed. Use this order every time instead of swapping the battery first.
Electricity leaves the positive terminal, passes the bulb and returns to the negative; break the path and the bulb goes out.
Scene 2: Conductors and insulators: the dividing line
Make a tester: cell, bulb and two wires with a gap at the ends. Clamp each item across the gap; a lit bulb means a conductor and an unlit bulb means an insulator.
Ask for predictions first, then test eight items: copper wire, iron nail, aluminium foil and salt water light the bulb, while rubber, a plastic ruler, glass and dry wood do not.
Name two boundaries. Distilled water hardly conducts, and water conducts once salt is dissolved in it. The human body contains salt water, which is exactly why wet hands near electrical fittings are dangerous.
That leads straight to why wires are coated: the copper carries the current and the plastic coating keeps the current from going anywhere else, including through your hand.
Ask for predictions first, then test eight items: copper wire, iron nail, aluminium foil and salt water light the bulb, while rubber, a plastic ruler, glass and dry wood do not.
Name two boundaries. Distilled water hardly conducts, and water conducts once salt is dissolved in it. The human body contains salt water, which is exactly why wet hands near electrical fittings are dangerous.
That leads straight to why wires are coated: the copper carries the current and the plastic coating keeps the current from going anywhere else, including through your hand.
Materials that conduct are conductors; those that do not are insulators, and the coating on a wire is an insulator.
Scene 3: Series and parallel: brightness and removing one bulb
Put two cells in series for 3 V. Light one bulb and note the brightness, then add a second bulb in series. Both go dimmer, because 3 V is now shared between two bulbs at about 1.5 V each.
Rewire in parallel: each bulb connects directly across the cell terminals, so each gets the full 3 V and both are about as bright as a single bulb.
Now the decisive test. Remove one bulb from the series pair and the other goes out, because the loop is broken. Remove one from the parallel pair and the other stays lit, because it has its own loop.
Add the short circuit in one line: a wire straight across the two terminals with no bulb in between lets a very large current flow, so the wire and the cell heat up. That is the science behind never pushing wire into a socket.
Rewire in parallel: each bulb connects directly across the cell terminals, so each gets the full 3 V and both are about as bright as a single bulb.
Now the decisive test. Remove one bulb from the series pair and the other goes out, because the loop is broken. Remove one from the parallel pair and the other stays lit, because it has its own loop.
Add the short circuit in one line: a wire straight across the two terminals with no bulb in between lets a very large current flow, so the wire and the cell heat up. That is the science behind never pushing wire into a socket.
Series shares the voltage and one removal puts both out; parallel gives each the full voltage and one removal leaves the other lit.
04 Question types and worked steps
| Type | Example | Steps | Answer |
|---|---|---|---|
| Fault finding | A connected circuit will not light; what is the most likely fault | Walk the four-step check from cell to bulb contacts to switch | One of the four is not making contact, most often a bulb contact |
| Sorting materials | Which two of copper, rubber, salt water and glass conduct | Test each across the gap and watch the bulb | Copper and salt water |
| Series and parallel | Two bulbs in series across 3 V: what does each get | Divide the total voltage by the number of identical bulbs | About 1.5 V each, so both are dimmer |
| Safety reasoning | Why are wet hands dangerous near a switch | Water with salt conducts, so the body becomes a path | Current can pass through the body, which is a shock risk |
Sanity check (teach this): Reasonableness check: two cells in series give 3 V, and two identical bulbs in series take about 1.5 V each, so the numbers must agree; an answer giving 3 V to each bulb has described parallel while using the word series. In series the current is the same everywhere, so the two bulbs are equally bright, and a claim that the first is brighter means series is not yet understood. That the remaining parallel bulb stays lit can simply be demonstrated rather than memorised. The body conducts because it contains salt water, so pure water is not a good conductor. Mains at 220 V is far above the 3 V used in class, and no experiment near a socket should ever be run, only described with pictures.
05 Independent practice (3 questions)
| Question | Answer | What to watch |
|---|---|---|
| Four-step check | List the four places you would check, in order, when a bulb will not light | Cell, both wire ends, both bulb contacts, switch |
| Testing | Predict then test aluminium foil, a plastic ruler, salt water and glass | Foil and salt water light the bulb; plastic and glass do not |
| Parallel | Two bulbs in parallel across 3 V; remove one, what happens to the other | It stays lit, because it has its own loop |
06 Common mistakes and what to say
| Mistake | Student writes | Say this |
|---|---|---|
| Swapping the battery first | Writes that a bulb that will not light means a flat battery | Before changing the battery, walk the four steps with me: battery direction, both wires clamped, both bulb contacts touching, switch closed. Most times it is a loose wire or a contact that is not touching. |
| Pure water as a conductor | Writes that all water conducts, so bathing is dangerous | Distilled water hardly conducts. It conducts once salt or impurities are in it. Your body contains salt water, which is why wet hands near an appliance are the risk. |
| Series treated as parallel | Writes that each of two series bulbs gets 3 V | In series the voltage is shared: 3 V between two bulbs is about 1.5 V each, so they dim. To give each bulb 3 V you need parallel. |
| Short circuit as brighter | Writes that a wire straight across the terminals makes the bulb brighter | With no bulb in between, the current is far too large, so the wire and cell get hot. That is a short circuit, and it is dangerous, not brighter. |
07 Homework (paper, section and question numbers)
- Primary 4 General Studies paper, Section C Basic science — Section C: circuit and conductor questions, marked against the answer sheet
- Primary 5 General Studies paper, Section C Science and Technology — Section C: a harder set on circuits and energy for a Primary 4 pupil who is ready
- Primary General Studies chapter index — Cross-check the science and technology chapter, forces and electricity section
08 Exit check (last 5 minutes)
| Question | Answer | Decision |
|---|---|---|
| What must be true for a bulb to light | A complete loop from positive through the bulb back to negative | Answering that a battery is enough means the loop is missing |
| Which of copper, rubber and salt water is not a conductor | Rubber | A wrong answer means judging by appearance; retest with the tester |
| Two bulbs in series, one removed: what happens to the other | It goes out, because the loop is broken | Answering that it stays lit confuses parallel; rerun the comparison |
09 Tutor FAQ
Does Primary 4 need voltage calculations?
No formula, but the relationship should be said in words: 3 V shared between two bulbs is about 1.5 V each. Whole numbers and halves are enough.
What if there is no equipment?
Two cells, two wires and two bulbs are enough, and a conductor tester can be built from the same parts. No kit needs buying.
How deep should short circuits go?
Only that with no bulb the current is too large and things get hot, with one real example. Leave resistance formulas to secondary school.
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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.