Choose the energy-transfer model that explains a given heating situation.
Loading saved practice…
Method and worked examples
Thermal energy transfers from higher to lower temperature. In conduction, interactions between neighbouring particles transfer energy without bulk movement of the material. Metals also have mobile electrons that help transfer energy. In convection, warmer regions of fluid are generally less dense and rise while cooler, denser regions sink, producing circulation. Convection requires bulk movement of a liquid or gas; it is not a process within an unmoving solid.
Radiation transfers energy by electromagnetic waves and can cross a vacuum. This explains energy reaching Earth from the Sun where conduction and convection cannot. Insulation reduces unwanted transfer; it does not create heat. A particle model is useful for contact transfer, while a wave model explains radiation without requiring moving material between source and receiver.
Example 1
A metal spoon handle warms while its tip is in hot soup. Classify the main transfer along the handle.
Conduction transfers energy through the solid metal. The spoon does not have to flow from the soup to the hand.
Example 2
Why can solar energy reach Earth through space?
Electromagnetic radiation crosses a vacuum. Conduction and convection require matter, so they cannot explain this transfer across space.
Watch out:The net thermal-energy transfer is from higher temperature to lower temperature.
Conduction, convection and radiation practice | Year 9 Science | Ascent Arcade