Investigating Electrical Conductors and Insulators

Electric current is the flow of charge around a closed circuit. Materials that let charges move easily are conductors. Materials that block charges are insulators. Think of charges like tiny cars: conductors are wide, open roads; insulators are solid walls.

Key ideas

• A complete circuit is needed for a bulb or buzzer to work.
• Metals are good conductors because some electrons are free to move.
• Plastics, rubber, dry wood, glass, and air are insulators because their electrons are tightly held.
• Graphite (pencil lead) conducts, even though it is not a metal. Tap water and salt water conduct; pure water conducts very poorly.

Simple investigation (bulb test)

Apparatus: battery (1–2 cells), small bulb or buzzer, switch, wires with crocodile clips, samples to test.

1. Build a simple series circuit with a small gap between two crocodile clips.
2. Place a material sample to bridge the gap and close the switch.
3. Observe: bright bulb = good conductor; dim bulb = poor conductor; no light = insulator. Record results in a table.

Making it a fair test

• Use pieces of similar size and shape.
• Clean metal surfaces; ensure firm contact with clips.
• Keep the same battery voltage for all tests.

Measuring more precisely

Add an ammeter in series to measure current. For the same battery, a larger current means lower resistance. This links to Ohm’s law: $I = \frac{V}{R}$. You can also place a voltmeter across the sample to compare $R$ values.

Expected results and special cases

• Metals (copper, aluminium, steel): conduct well.
• Graphite: conducts; useful to test with a pencil lead.
• Plastics, rubber, dry wood, glass: insulators.
• Liquids: tap water/salt water conduct; pure water and oil are poor conductors.
• Wet materials conduct better than dry versions (e.g., wet wood).

Safety

• Use low-voltage cells only; never use mains electricity.
• Keep liquids away from the battery and switch; dry hands before testing.
• Do not short the battery (connect clips directly together) for long periods.

Real-world connections

• Cables: metal cores for conduction, plastic coating for insulation.
• Plugs and tools: metal parts to carry current, plastic casings to protect users.
• Pan handles are often plastic/wood to stop heat and electricity reaching your hand.

Common misconceptions

• “Water always conducts.” Only if it has dissolved ions (tap or salt water). Pure water is a poor conductor.
• “Only metals conduct.” Graphite and salty solutions also conduct.
• “If the bulb is off, the circuit is wrong.” It may be correct, but the sample could be an insulator.