Energy transfer by conduction, convection and radiation, and a thermal conductivity measurement

The idea

A hot object loses energy by particle collisions through a solid, by bulk flow of a fluid, and by electromagnetic radiation, at rates set by the material and the temperature difference.

Safety card

What you need

• Conduction: rods of copper, aluminium, brass and steel of equal length with wax-held drawing pins, beaker of hot water
• Convection: large beaker of water, a crystal of potassium permanganate dropped down a tube, Bunsen and tripod
• Radiation: two identical cans, one matt black and one shiny, with a thermometer or temperature probe for the water in each; an infrared thermometer; or a Leslie cube
• Conductivity (NSW Department of Education Module 3 guide, Activity 13): vacuum flask of just-boiled water with thin plates of steel, aluminium, glass and plastic laid over its mouth, an ice cube on each, balance and stopwatch

How to do it

1. Conduction: stand the rods in the hot water and time the drop of each pin; rank the metals.
2. Convection: heat one side of the beaker gently and watch the coloured stream rise, cross and sink.
3. Radiation: fill the black and shiny cans with equal volumes of hot water from the same kettle, put a thermometer or probe in the water of each and read both every minute for ten minutes. Then aim the infrared thermometer at each can's outer surface: the shiny can reads well below the water inside it because a shiny surface emits far less infrared at the same temperature, so the infrared thermometer shows the difference in emission but cannot measure the shiny can's temperature.
4. Conductivity: weigh an ice cube, place it on the plate over the flask and time it to melt; compute the energy from the latent heat and the conductivity from Q/t = k A delta T / d.

What you should see

Pins fall first from copper (k = 385 W/(m K)), then aluminium (205), brass (109) and steel (50.2). The thermometers in the water show the black can cooling faster than the shiny one, and the infrared thermometer reads the shiny surface well below the water temperature while it reads the black surface close to it. The idealised model, with a 90 degree difference, a little under the 100 degrees between just-boiled water and melting ice, across a 1.0 mm plate of 10 cm^2, gives 4.5 kW through steel (melting a 20 g cube, 6.7 kJ, in 1.5 s) and 72 W through glass (k = 0.8, about 93 s). Real melting takes far longer on every plate, because the rate is also limited by how fast the flask's water and steam deliver energy to the plate and by the contact with the ice, so the learner compares the measured conductivities with the table values and explains the gap.

What changes

What you change

material of the plate

What you measure

time for the ice to melt (rate of conduction)

What you keep the same

• plate thickness and area
• temperature difference
• ice mass

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• Metal feels cold because it is colder than wood; both are at room temperature and metal conducts energy from the hand faster.
• Heat rises; hot fluid rises because it is less dense, while radiation and conduction go in every direction.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Physics Stage 6 Syllabus (2017), current: Year 11 until the end of 2026, Year 12 until Term 3 2027PH11-10PH11/12-3PH11/12-6
• Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

1. www.nsw.gov.au/sites/default/files/noindex/2025-03/physics-stage-6-syllabus-2017.docx
2. education.nsw.gov.au/content/dam/main-education/teaching-and-learning/curriculum/key-learning-areas/science/s-6/physics/Physics-module-3-guide.docx
3. hyperphysics.gsu.edu/hbase/Tables/thrcn.html
4. hyperphysics.gsu.edu/hbase/Tables/phase.html