Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
What is Electricity?
Electricity is the flow of electric charge (electrons) through a conductor. We use electricity to light bulbs, run fans, power phones, and much more.
Electric Cell
- An electric cell converts chemical energy → electrical energy.
- Has two terminals:
- Positive terminal (+) — represented by a longer thin line in circuit symbol.
- Negative terminal (−) — represented by a shorter thick line.
- Common examples: torch cell (dry cell), button cell in watches.
- A battery = two or more cells connected together.
Electric Circuit
An electric circuit is a complete path along which electric current flows.
Parts of a Simple Circuit
| Component | Role |
|---|---|
| Electric cell | Source of electricity |
| Wires | Carry current from cell to bulb and back |
| Bulb | Converts electrical energy to light |
| Switch | Opens or closes the circuit |
Open vs Closed Circuit
| Type | Switch Position | Current Flows? | Bulb |
|---|---|---|---|
| Closed circuit | ON (closed) | Yes | Glows |
| Open circuit | OFF (open) | No | Does not glow |
Electric Bulb
- Has a thin wire inside called the filament made of tungsten.
- Filament glows when current passes through it.
- The glass is filled with inert gas (argon) or is a vacuum to prevent the filament from burning.
- The two ends of the filament are connected to the two terminals at the bottom of the bulb.
Conductors and Insulators
Conductors
Materials that allow electric current to flow through them.
Examples: Copper, iron, aluminium, steel, silver, gold, saltwater.
Insulators
Materials that do not allow electric current to flow through them.
Examples: Rubber, plastic, wood, glass, dry air, pure water, thermocol.
Why do electricians use rubber gloves? Rubber is an insulator — it protects them from electric shock.
Circuit Symbols
| Component | Symbol Description |
|---|---|
| Cell | Long thin line (+) and short thick line (−) |
| Battery | Multiple cell symbols in a row |
| Bulb | Circle with a cross or X inside |
| Switch (open) | A break in the line |
| Switch (closed) | A line completing the circuit |
| Wire | Straight lines connecting components |
Testing Conductors and Insulators
Simple circuit tester:
- Make a circuit with a cell, bulb, and two free wire ends.
- Touch the two ends to a material.
- Bulb glows → material is a conductor.
- Bulb does not glow → material is an insulator.
Materials to test: iron nail, coin, pencil (graphite tip), rubber, plastic, wooden stick.
Results:
- Iron nail → conductor (bulb glows).
- Rubber eraser → insulator (bulb doesn't glow).
- Pencil tip (graphite) → conductor (bulb glows) — surprising for students!
Key Vocabulary
| Term | Meaning |
|---|---|
| Electric cell | Device that produces electricity from chemicals |
| Circuit | Complete path for electric current |
| Conductor | Allows current to flow |
| Insulator | Does not allow current to flow |
| Switch | Device to open or close a circuit |
| Filament | Thin wire inside a bulb that glows |
| Terminal | End point of a cell (+ or −) |
| Battery | Two or more cells connected |
Exam Tips
- Two terminals of a cell — positive and negative — basic 1-mark fact.
- Bulb only glows in a complete (closed) circuit — explain why in short answers.
- Give at least 3 conductors and 3 insulators for 3-mark answers.
- Graphite (pencil tip) is a conductor — this surprises many students; remember it.
- A battery is multiple cells — not just a single cell.
- Know the function of each component in a simple circuit.