CHEMISTRY · Stage 7 · Chapter 3: Metals and Non-Metals
Chemistry 3.2 Comparing conductors — Thermal and Electrical Conductivity
5 min read 7 parts Lesson 2 of 7
Lesson summary
3.2 Comparing conductors — Thermal and Electrical Conductivity — Alhussan International Academy — Chemistry (Stages 7–9) notes: Plan and evaluate a fair-test investigation to compare how well metals conduct thermal energy and electricity.Conductor = a material that allows energy …
- Explanation
- Scientific question
- Controlling variables
- Prediction
- Accurate data
- Reliable data
Section 1 of 7Conductors and insulators
- Conductor = a material that allows energy or charge to move through it easily.
- Thermal conductors transfer thermal energy well and electrical conductors let an electric current flow.
- Insulator = a material that does not conduct well.
- Pattern
- most metals are good thermal and electrical conductors and most non-metals are poor conductors.
- Graphite, a form of carbon, is a non-metal that conducts electricity.
- Silver is the best conductor, followed by copper, which is why copper is used in electrical wires.
- Explanation
- metals contain delocalised (free) electrons that carry charge and pass on energy quickly.
Section 2 of 7Why heat sinks matter
- Heat sink
- a metal part in a computer that transfers thermal energy away from the processor and stops it getting too hot.
- Question
- some computers have aluminium heat sinks and others copper, so which metal is better, and why are iron and zinc not used?
Section 3 of 7Asking a scientific question and planning
- Scientific question = a question that can be answered using evidence.
- "Which heat sink is better?" is not scientific, but "Which conducts thermal energy quickest — aluminium, copper, iron or zinc?" is.
- Apparatus
- four metal strips with a drawing pin attached to each by wax, heated at the same end by one candle.
- As thermal energy travels along the strip the wax melts and the pin drops off.
- The time from lighting the candle to each pin falling is measured.
- Fair test
- only one variable changes.
| Type of variable | Meaning | In this investigation |
|---|---|---|
| Independent | The quantity changed | Type of metal |
| Dependent | The quantity that changes in response | Time for pin to fall off |
| Control | Variables kept the same | Size of metal strip, amount of wax, amount of heat |
- Controlling variables
- measure the strips to check their size and weigh the same mass of wax.
- The same candle heats all four metals at once, so the thermal energy supplied is equal.
- Safety
- take care when lighting the candle and let hot metals cool before touching them.
Section 4 of 7Prediction, accuracy and reliability
- Prediction
- data books show that copper conducts best, followed by aluminium, then zinc, with iron the lowest, so the pin on the copper strip should drop first.
- Accurate data = data close to the true value, helped by starting the timer when the candle is lit and noting the time each pin falls.
- Reliable data = data obtained by making enough measurements, so repeat the whole experiment three times and calculate means.
- Conclusion
- a bar chart shows the pin drops off copper first,
- so copper conducts thermal energy best,
- which explains why heat sinks are made of copper or aluminium and not iron or zinc.
Section 5 of 7Investigating electrical conductivity
- Build a simple circuit with a cell, a lamp or ammeter and a gap where materials can be connected.
- Connect copper, iron, aluminium, graphite, plastic and wood in turn.
- A brighter lamp or larger current shows a better conductor.
- Results
- metals and graphite complete the circuit, while plastic and wood do not.
Section 6 of 7Analysing results
- Present results in a table and plot a bar chart, because the metals are categories.
- Errors
- uneven heating, rods of different thickness and drawing pins of different mass.
- Conclusion
- state the best conductor, quote the data and explain using free electrons.
| Material | Thermal | Electrical |
|---|---|---|
| Copper | Very good | Very good |
| Iron | Good | Good |
| Plastic | Poor | Poor |
| Graphite | Moderate | Good |
Section 7 of 7Applications of conductors
- Copper
- it is used in electrical wires and cooking pans because it conducts heat and electricity well and is ductile.
- Aluminium
- it is used in overhead power cables because it conducts well and has a low density.
- Plastic
- it coats wires as a safe insulator.
- Polystyrene and wool
- they trap air and reduce heat loss.
- Justifying a choice
- state the property, say why it matters for the use and give the material.
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