Electric Circuits, Grade 8
A cell does not store electricity. It stores chemicals that push charge around a loop.
You will see it written that electrical energy is stored in a cell. It is not, and the difference matters: a learner who thinks a cell is a bucket of electricity cannot explain why the circuit has to be a closed loop, or why a flat cell weighs exactly the same as a fresh one.
This page covers the components, how to draw a circuit diagram that earns its marks, and the three things a current does. For what happens when you wire bulbs one after another or side by side, see our series and parallel circuits practical.
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 8 |
| Term | 3 |
| Strand | Energy and change |
| Topic | Energy transfer in electrical systems |
| Status | Informal activities. The assessed Term 3 task is the electromagnet project |
| Marks | 50 on our worksheet. None prescribed |
The components
| Component | What it does |
|---|---|
| Cell | Pushes charge around the circuit. One unit |
| Battery | Two or more cells joined together. Not another word for a cell |
| Conducting wire | Carries charge with very little resistance |
| Switch | Breaks the loop to stop the current |
| Bulb | Turns electrical energy into light and heat |
| Resistor | Opposes the current |
How to draw a circuit diagram
Five rules, and they are where the marks are.
- Straight lines and square corners, in a rectangular loop
- Components drawn on the lines, not floating next to them
- Correct symbol for every component
- The long line of the cell is positive. This is the one learners reverse most often
- No gaps, unless a switch is deliberately drawn open
The commonest error is drawing the apparatus. A picture of the battery, the wires and the bulb as they look on the bench is not a circuit diagram, and where a diagram is asked for it scores nothing.
Two bulb symbols are in use: a circle with a cross, and a circle with a filament loop. The curriculum uses the crossed circle, and both turn up in past papers.
Practical 1: build a circuit that works
You need: two AA cell holders, a 2,5 V bulb in a holder, a switch and four crocodile leads.
- Connect cell to switch to bulb and back to the cell. One loop
- Close the switch. The bulb lights
- Open it. The bulb goes out
- Now remove any one lead. Nothing works, although everything else is still connected
That last step is the lesson. A circuit is not a collection of parts. It is a loop, and one gap anywhere stops all of it.
Practical 2: the heating effect, done safely
A version of this activity in circulation tells learners to create a short circuit, leave it two minutes, then touch the wires to feel which is warmer. We do not print that. A shorted cell heats fast, can vent or leak, and short circuits are what start house fires.
You need: two cells, a switch, crocodile leads and 10 cm of 0,15 mm nichrome wire.
- Clip the nichrome into the loop so the current runs through it
- Close the switch for ten seconds, then open it
- Feel the nichrome carefully, then feel a copper lead for comparison
- Repeat with 5 cm of nichrome
The nichrome is warm. The copper is not. Both carry exactly the same current, so the difference is resistance: nichrome has far more of it, and that is where the electrical energy is turned into heat.
The shorter piece gets hotter, because less wire means less resistance, which means more current. That is a filament explained in one bench test, and it is why a heater element is nichrome and the wire feeding it is copper.
Ten seconds at a time, and open the switch between tries.
Practical 3: the magnetic effect
You need: a cell, a switch, one long lead and four small compasses.
- Lay the lead out north to south and put the compasses along it
- Note which way they all point
- Close the switch. They swing
- Turn the cell around. They swing the other way
A current makes a magnetic field, and reversing the current reverses the field. If the movement is small, thread the wire through a hole in card three or four times and stand the compasses close in: one straight wire on two cells is a weak field.
This is the effect the whole electromagnet project is built on, so it is worth doing before that project rather than after it.
Practical 4: the chemical effect
A current passed through a solution can break it apart. That is electrolysis, and it is how water is split into hydrogen and oxygen.
The version printed in most places uses plain warm water and no electrolyte. Water on its own barely conducts, so a class sees a bubble or two and learns nothing. Five grams of bicarbonate of soda in 200 ml fixes it.
The full method is on our atoms, elements and compounds practical, including why the salt version of this experiment should not be used: it makes chlorine.
Conductors, insulators and resistance
Test three conductors in the same bulb circuit.
| Conductor | Bulb |
|---|---|
| Copper | Brightest |
| Iron or steel wire | Slightly dimmer |
| Nichrome | Dimmest |
All three conduct. What differs is how much they resist, and nichrome resists most, which is why it heats rather than carries.
Never use steel wool for this comparison. Fine steel strands across a battery glow and catch alight; it is a standard way to start a fire. Steel or iron wire gives the same result and does not burn.
Fuses, and what South African homes actually have
A fuse is a thin wire that melts when too much current flows, breaking the circuit. Once it has melted it must be replaced.
Most South African homes have not had fuses in the board for decades.
| Device | What it does | Where you find it |
|---|---|---|
| Circuit breaker | Trips, and can be switched back on. Protects the wiring from too much current | The distribution board |
| Earth leakage | Trips when current escapes to earth, for example through a person. Protects people, not wiring | The distribution board |
| Fuse | Melts, and is replaced | Plugs, cars, some appliances |
Send the class home to look at their own distribution board. They will find breakers and an earth leakage switch, and being able to explain their own house is worth more than memorising a fuse.
Short circuits, and one question that should not be set
A short circuit is a path that lets current bypass the components with almost no resistance. A very large current flows, the wires heat, and that is how electrical fires start.
Used deliberately and safely, the same idea is useful: in a battery circuit with a burnt-out bulb, a wire connected across that bulb completes the loop again and everything else works.
You may meet a question asking learners to draw how to create a short circuit so that an electric kettle with a broken indicator light keeps working. It should not be set.
- A kettle runs on 230 V mains. Opening one and bypassing a component can electrocute you or start a fire
- It is not a short circuit in any case. What is meant is shorting out the indicator lamp
- Mains appliances are repaired by a qualified electrician, and that is the answer a learner should give
If it does not work
| Problem | Cause | Fix |
|---|---|---|
| Nothing happens at all | A crocodile clip is gripping insulation | Clip bare metal, and check every joint |
| The circuit looks right but the bulb is dark | Flat cells, or a blown bulb | Swap the bulb first. It is the cheaper test |
| It works, then stops | A clip has slipped off a round terminal | Press it on firmly |
| The nichrome does not warm up | Too long a piece, or only one cell | 10 cm and two cells, then try 5 cm |
| The compasses barely move | One straight wire is a weak field | Loop the wire three or four times, compasses close in |
| Everything works but the bulb is dim | Tired cells | Fresh cells |
Safety
- Nothing in this topic plugs into a wall. Cells only
- Never connect a wire straight across a cell. That is the short circuit this page refuses to demonstrate
- Never use steel wool as a conductor
- Nichrome gets hot. Ten seconds at a time, and let it cool before handling it
- Open the switch between tests. A closed switch flattens cells and keeps the wire hot
- Two AA cells, not a 9 V block
How the 50 marks are made up
| Section | Marks |
|---|---|
| Components | 12 |
| Circuit diagrams | 12 |
| The effects of a current | 14 |
| Conductors and resistance | 6 |
| When things go wrong | 6 |
Nothing is prescribed for this topic. The worksheet and this split are ours.
Free worksheet and marking memo
Both free, no sign up, straight to the PDF.
- Learner worksheet, 50 marks, with two circuit diagrams to draw, the nichrome results table and the kettle question
- Marking memorandum, with what to accept for each answer and the five answers that look right and score nothing
Related practicals
- Series and parallel circuits, Grade 9. The same components, wired two different ways, and what happens to the brightness
- Make and use an electromagnet, Grade 8. The assessed Term 3 project, built on the magnetic effect above
- Atoms, elements, compounds and mixtures, Grade 8. The chemical effect, with the electrolyte that makes it work
What you need to run it
A class set for six groups comes to about R404, and every line is cheap and deep: bulbs at R6, holders at R5, switches at R6,35 and cell holders at R6,50, plus a pack of crocodile leads.
The one specialised item is nichrome wire at R40 for 10 m, which is enough for a hundred pieces and turns the heating effect from a description into a measurement.
For a single learner building a project at home, the light circuit kit at R30 has the globe and switch in one packet.
The rest of the range is in electric circuit kits and apparatus.