Physics 11–12 · Year 11

How hot is a Bunsen flame? Specific heat applied to a heated metal cylinder

Module 3: Waves and Thermodynamics (Thermodynamics)

PracticalMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

The idea

A hot metal dropped into water reaches thermal equilibrium, and energy conservation lets the metal's starting temperature be found from the water's rise.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

Bunsen flame
very hot metal
steam splash on transfer

Controls

tongs and heat mat
safety glasses
tie back hair, keep the cup away from the flame

Note

Heat and hot liquids: record the activity in RiskAssess (https://www.riskassess.com.au/) and follow the Science ASSIST risk management information sheet (https://asta.edu.au/resource/ais-risk-management-and-risk-assessment/).

What you need

Iron or stainless-steel cylinder of about 50 g on a wire loop (the NSW Department of Education Module 3 guide, Activity 14, recommends these metals for their high melting points and warns that aluminium may melt in the flame), tongs, Bunsen burner, heat mat, tripod
Polystyrene cup with 0.200 kg of water, thermometer to 0.1 degree, electronic balance

How to do it

Weigh the cylinder and the water; record the water temperature.
Hold the cylinder in the hottest part of the flame for a fixed time of about 30 s, as the NSW Department of Education Module 3 guide (Activity 14) suggests; a 50 g cylinder is still heating at 30 s, so time every heating and keep it the same.
Transfer it quickly into the water, stir, and record the highest temperature.
Equate energy lost by the metal to energy gained by the water and solve for the flame temperature.
Pool class results and discuss the spread with a box plot; repeat with improvements, including a longer heating time such as 60 s, and check whether the inferred temperature still rises: it stops rising only once the cylinder has reached a steady temperature in the flame.

What you should see

With a 50 g iron cylinder and 0.200 kg of water warming from 20.0 to 28.0 degrees, the water gains 6698 J. Taking iron's heat capacity at 25 degrees Celsius (449 J/(kg K), from the NIST-JANAF data) the cylinder started near 326 degrees Celsius; because iron's heat capacity rises with temperature (574 J/(kg K) at 327 degrees Celsius), integrating the NIST data gives a lower start of about 293 degrees Celsius. The class spread is wide, as the Module 3 guide notes, because the metal is still heating when it leaves the flame after 30 s, cools during transfer, never reaches the flame's own temperature, and the flame temperature varies with position; the learner knows the method worked when the energy balance closes and the improved repeat narrows the spread.

What changes

What you change: position of the cylinder in the flame
What you measure: final water temperature and inferred metal temperature
What you keep the same: mass of water
mass of metal
transfer time
heating time

Common misconceptions

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

The final temperature is the average of the two starting temperatures; it depends on the masses and specific heats.
The metal loses more energy than the water gains; in an insulated cup they are equal.

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 2027PH11-10 PH11/12-4 PH11/12-6
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities