Will Electricity Flow Through It?
An electric conductor allows current to flow through it easily.
An electric insulator resists the flow of current.
Why Do Metals Conduct?
Metal atoms have free electrons that can drift along when a voltage is applied. The moving electrons carry the electric charge.
Testing Materials
A simple test circuit uses a battery, bulb, and two leads. Insert the material between the leads — if the bulb lights, it conducts.
| Conductors | Insulators |
|---|---|
| Copper | Rubber |
| Aluminium | Plastic |
| Iron / Steel | Wood (dry) |
| Graphite (carbon) | Glass |
| Salt water | Pure water |
Pure water is actually an insulator; it's the dissolved salts and minerals in tap water that allow conductance.
Everyday Uses
Conductors in use:
- Copper wires carry current inside cables
- Aluminium used in electricity pylons (lightweight + good conductor)
Insulators in use:
- Plastic coating on cables prevents shock
- Rubber gloves for electricians
- Ceramic or glass insulators on pylons
Why is the wire inside a plug copper but the outer cable is plastic?
Copper conducts electricity to the device. The plastic coating prevents the current from reaching anything you touch — protecting you from electric shock.
Real world: household electrical wiring
The wiring inside a house uses copper conductors (low resistance, efficient current flow) sheathed in PVC plastic insulation (prevents shock if the cable is touched). A typical 2.5 mm² copper wire safely carries up to 27 A. The choice of conductor and insulator is a critical safety decision in every electrical installation.
Real world: high-voltage power transmission lines
National grid transmission lines use aluminium conductors (lightweight, good conductor, cheaper than copper) for the cores. The ceramic insulators on the pylons prevent current leaking to the steel structure. This material selection — conductor for the core, insulator for the mounting — is the direct application of conductivity principles.
Real world: electronic circuit board
A printed circuit board (PCB) uses copper tracks (conductors) to connect components, with a fibreglass epoxy board (insulator) as the base. Soldering iron tips are copper (conducts heat well); handles are plastic (insulates from heat). Understanding conductors and insulators is fundamental to electronics design.
Practice Problems
A nail, a rubber band, a pencil lead, and a piece of glass are tested in a circuit. Which ones will light the bulb?
Show answer
Why are electrical cables not made from iron?