Comparing Rates of Cooling Experiment

This experiment investigates how different surfaces emit thermal radiation at different rates.

Method (Leslie’s cube or equivalent)

1. Fill identical containers (e.g. metal cans) with the same volume of hot water at the same starting temperature.
2. Vary ONE factor:
   • Surface colour: one black, one white, one shiny
   • Or surface area: different shapes but same volume
3. Record the temperature at regular intervals (e.g. every minute for 20 minutes).
4. Plot temperature against time for each container.

Expected results

The container that cools fastest has the steepest cooling curve.

Surface colour and texture:

• Dark, matt surfaces cool fastest (they are the best emitters of infrared radiation).
• Light, shiny surfaces cool slowest (they are the poorest emitters).

Surface area:

• Larger surface area cools faster (more area to emit radiation).

Controlling variables

• Same volume and type of liquid.
• Same starting temperature.
• Same room temperature and position (away from draughts).
• Same type of lid (or no lid) to control convection.
• Only one variable changed at a time.

Why this matters

These results explain why:

• Car radiators are painted black (good emitters).
• Survival blankets are shiny (poor emitters and good reflectors).
• Teapots are often shiny (to keep tea hot longer).
• Solar panels are dark (good absorbers).

Common errors and how to correct them

• Not controlling starting temperature (all containers must begin at the same temperature).
• Placing containers at different distances from walls or windows (creates unequal convection).

How to apply this in an exam

Describe the measurements (temperature at intervals), the control variables, and what the gradient of the cooling curve tells you about emission rate.