2. Conduction

Learning outcomes

  • I can describe conduction as heat transfer through direct particle collisions.

  • I can explain why conduction is most effective in solids.
  • I can compare thermal conductors and thermal insulators.
  • I can identify materials with high and low thermal conductivity.
  • I can apply conduction concepts to real-world situations.

Thermal Conductors and Insulators

Materials that allow heat to pass through them quickly are called good thermal conductors. Metals such as copper, aluminium, silver, and steel are excellent examples — they are used for cooking pans, radiators, and the bases of kettles because they transfer heat efficiently.
Materials that slow the transfer of heat are called thermal insulators or poor conductors. Wood, plastic, rubber, glass, wool, and many foams are common insulators; they are used for saucepan handles, refrigerator doors, or building insulation to keep heat in or out.

How Conduction Works in Solids

In solids, the particles (atoms or molecules) are tightly packed in a regular arrangement called a lattice. When one part of a solid is heated, those particles vibrate faster. Their vibrations pass along the lattice, transferring energy from particle to particle — this is thermal conduction by lattice vibrations.
Metals conduct heat much more efficiently than non-metals because, in addition to lattice vibrations, they have delocalised (free) electrons that move easily through the metal. These electrons carry energy quickly from hot regions to cooler ones, making metals the best thermal conductors.

Thermal Conduction

A. Key Ideas

  1. Define thermal conduction in your own words.

  2. Give two examples of good thermal conductors and two poor conductors (insulators).

  3. Why are saucepan handles often made of plastic or wood instead of metal?

  4. Metals are better thermal conductors than non-metals. Explain why, using the idea of delocalised electrons.

B. Understanding the Lattice

  1. Draw a simple diagram of particles in a solid showing how lattice vibrations transfer energy. Label your diagram.

  2. Why is conduction usually slower in non-metals than in metals?

  3. If a 15 cm metal rod and a 15 cm wooden rod are heated at one end, which one will get hot at the other end first? Explain.

C. Real-World Links

  1. A company is designing a cooking pot. Which material would you suggest for the pot body and which for the handle? Give reasons.

  2. Name one situation where it’s useful to prevent conduction and one where it’s useful to encourage it.

  3. A student says, “Styrofoam keeps drinks warm because it generates heat.” Correct this misunderstanding.

Convection

A. Concepts

  1. Define convection.

  2. Convection happens only in liquids and gases, not in solids. Why?

  3. What property of a liquid or gas changes when it is heated, allowing convection currents to form?

B. Explaining the Process

  1. Use the words density, rise, sink, and current to describe what happens when water at the bottom of a beaker is heated.

  2. Draw and label a diagram showing convection currents in a pan of water being heated from below.

  3. Describe how convection helps a radiator heat a room.

C. Applications

  1. Sea breezes are an example of convection. Explain how they form during the day.

  2. Why does a refrigerator have a cooling unit at the top and not at the bottom?

  3. A hot-air balloon rises when the air inside is heated. Explain this using density.

  4. List three everyday examples where convection transfers heat.