Course: Separate Physics only | Tier: Foundation + Higher
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Aim
To investigate how effective different materials are as thermal insulators, and how the thickness of a material affects its insulating properties.
Method
- Place a small beaker inside a larger beaker.
- Fill the small beaker with hot water from a kettle and cover it with a cardboard lid with a hole for the thermometer.
- Record the starting temperature, then the temperature every 3 minutes for 20 minutes.
- Repeat with different materials packed between the beakers (e.g. newspaper, bubble wrap, cotton wool), keeping the volume and starting temperature of the water the same.
- For thickness: repeat with different numbers of layers of the same material.
- Plot cooling curves (temperature against time) for each material.
| Independent variable | Type of material (or number of layers) |
| Dependent variable | Temperature of the water over time |
| Control variables | Volume of water; starting temperature; time interval; size of beakers |
Questions
Q1 (F) Name the independent and dependent variables when comparing materials.
Show answer
Independent: type of insulating material. Dependent: temperature of the water (after a set time), or how quickly it cools.
Q2 (F) Give two control variables.
Show answer
Any two of: volume of water; starting temperature of the water; thickness of material; time interval between readings; size of beakers.
Q3 (F) Why is a lid placed on the small beaker?
Show answer
To reduce energy lost from the top of the water by evaporation and convection, so the test compares only the insulating material.
Q4 (F) State one hazard and how to reduce the risk.
Show answer
Hot water can scald. Pour carefully, stand the beakers on a heatproof mat, and don’t move beakers full of hot water.
Q5 (F/H) The water cools from 80 °C to 62 °C in 15 minutes. Calculate the mean rate of cooling.
Show answer
Temperature drop = 80 − 62 = 18 °C
Rate = 18 ÷ 15 = 1.2 °C per minute
Q6 (F/H) How can you tell from the cooling curves which material is the best insulator?
Show answer
The best insulator has the shallowest curve – the smallest temperature drop in the same time.
Q7 (F/H) Explain why the water cools fastest at the start.
Show answer
At the start the temperature difference between the water and the surroundings is largest, so the rate of energy transfer to the surroundings is highest. As the water cools, the difference gets smaller and it cools more slowly.
Q8 (H) Suggest two improvements to make the results more accurate.
Show answer
Any two of: start the timer when the water reaches exactly the same temperature each time (e.g. 80 °C); use a temperature probe and data logger to record continuously; repeat each test and calculate a mean; keep the room temperature the same.
