IGCSE Physics / Thermal energy
Practical: investigating conduction, convection and radiation revision notes
Edexcel International GCSE Physics (4PH1), chapter 15: Thermal energy, specification point 4.9. Free lesson.
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These practicals show how to investigate conduction, convection and radiation. They also show how to make a fair comparison by controlling variables and working safely.
How to compare metals as conductors
Heat copper, aluminium and steel rods equally. Energy travels along each rod and melts the wax holding a pin at its far end. A better conductor transfers energy faster, so its pin falls sooner. Use rods with the same length and thickness, and fix a pin to each far end with wax. The first pin to fall marks the best conductor. A longer time means a poorer conductor. Copper usually comes first and steel last. Do not touch the hot rods. Leave them on a heatproof mat to cool.
How to make a convection current visible
A small crystal of potassium manganate(VII) colours the water purple, making its movement visible. Water heated beneath the crystal rises, then moves across the top and sinks on the far side. This circulating movement is a convection current. Use a beaker of cold water and one small crystal, placed at the bottom against one side. Heat gently directly under the crystal. The purple colour rises above the flame, crosses the top and sinks at the far side. The crystal stains skin and is harmful. Use tweezers, not fingers, and use only a tiny crystal.
How to compare surfaces as emitters
This practical compares how quickly surfaces emit infrared radiation. If the cans begin under the same conditions, the one with the greater temperature drop loses energy faster. The dull black can cools faster, so it is the better emitter. Use two identical metal cans: one dull black and one shiny silver. The independent variable is the surface type. The dependent variable is the temperature drop in 10 minutes, read from the thermometers. Keep the volume of water and starting temperature the same. More water takes longer to cool, and a hotter can loses energy faster. Use identical cans so…
How to make the rod comparison fair
The pins fall when enough energy has travelled along each rod to melt its wax. If one rod is heated for longer, it receives more energy, so its pin might fall sooner for that reason rather than because its metal conducts better. Heat all rods equally so that the metal is the only difference. The shortest time shows the best conductor. The longest time does not show the best conductor; it indicates a poorer conductor.