Science 7–10 · Year 8
Conduction: which metal carries heat fastest
Physical sciences — Change, content group Energy transfers (NSW Stage 4 focus area)
School laboratory, not for home
In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
The idea
Thermal energy passes along a solid from the hot end to the cold end at a rate that depends on the material, with copper conducting far faster than steel.
Safety card
Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
Hazards
- burns from hot rods and the hub, which stay hot for many minutes
- naked flame
- hot wax
Controls
- eye protection and tied-back hair
- heat-resistant mat and gloves
- rods handled only after cooling
- flame turned off as soon as the last pin drops or five minutes have passed
Note
Heat or electrical energy is involved. Complete the school's risk assessment for the activity before the lesson, using CSIS 1.7 (Risk assessment – a pre-requisite for risk control) from the department's Chemical Safety in Schools package (2021 Technical Update), which the NSW Department of Education Science safety and compliance page names for risk assessment advice.
What you need
- conductivity apparatus: rods of copper, aluminium, brass and steel of equal length and diameter fixed to a central hub, 1 (or four separate 150 mm rods in a clamp)
- candle wax or petroleum jelly, a small amount
- drawing pins, 8
- Bunsen burner, tripod and heat-resistant mat, 1 set
- stopwatch, 1
- heat-resistant gloves, 1 pair
- eye protection for all
How to do it
- Stick a drawing pin with a small blob of wax halfway along each rod and a second pin at its free end, twice as far from the hub; use the same two positions on every rod.
- Set the apparatus on the mat with the hub over the Bunsen and heat the hub with a blue flame.
- Start the stopwatch as heating begins and record the time at which each pin drops. Continue until all pins have dropped or five minutes have passed.
- Rank the metals from fastest to slowest conductor by the drop times of the halfway pins.
- Compare each rod's halfway-pin time with its end-pin time.
- Allow the apparatus to cool completely before touching it.
What you should see
Copper's pins drop first, then aluminium, then brass, and steel last, taking much longer than copper; this order follows the metals' thermal conductivities. On each rod the end pin, twice as far from the hub, takes more than twice as long as the halfway pin. The main reason is that heat spreading along a rod has to warm all the metal on the way, so its spread slows the further it travels; heat escaping from the rod's sides lengthens the time further. A pin that has not dropped within five minutes, most often the end pin on steel, is recorded as not dropped rather than left blank. The learner knows it worked when the order copper, aluminium, brass, steel is repeatable between groups.
What changes
- What you change
- metal of the rod
- What you measure
- time for the wax to melt and the pin to drop (s)
- What you keep the same
- rod length and diameter
- same pin positions on every rod
- same flame setting and position
- same amount of wax
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Metals feel cold because they are at a lower temperature.
- Heat travels along a rod like water through a pipe, all at once.
- All metals conduct equally well.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Science 7–10 Syllabus (2023)SC4-CHG-01SC4-WS-04SC4-WS-06
- Australian Curriculum v9AC9S8U05AC9S8I02AC9S8I05
Sources
The pages the author read to write this activity.