Time / min Temp (with lid) / °C Temp (without lid) / °C 0 78 78 3 74 72 6 70 62 9 66 56 12 61 52 In an investigation, a student places a lid of aluminium fo...
Question 1 Report
| Time / min | Temp (with lid) / °C | Temp (without lid) / °C |
|---|---|---|
| 0 | 78 | 78 |
| 3 | 74 | 72 |
| 6 | 70 | 62 |
| 9 | 66 | 56 |
| 12 | 61 | 52 |
In an investigation, a student places a lid of aluminium foil over a beaker of hot water. A second identical beaker of hot water is left without a lid. Both beakers start at 78 °C. The student records temperatures every 3 minutes for 12 minutes.
Table 20.1 shows the results.
(a) State which beaker cools faster. Use data from the table to support your answer. [2]
(b) State two methods of heat transfer that the foil lid reduces. [1]
(c) Explain why the beaker without a lid loses heat faster from the surface. [2]
(d) Calculate the temperature drop of the open beaker in the first 6 minutes. [1]
(e) Suggest one variable the student must control. [1]
Answer Details
(a) The beaker without the lid cools faster. [1] After 12 minutes, the open beaker has cooled to 52 °C while the lidded beaker is at 61 °C. That is a total drop of 26 °C for the open beaker compared to only 17 °C for the lidded beaker, a difference of 9 °C. [1]
(b) The foil lid reduces two methods of heat transfer: convection (warm air cannot rise freely from the water surface) and evaporation (the lid traps water vapour, slowing the rate at which molecules escape from the liquid surface). [1]
(c) Without a lid, the beaker loses heat faster from the surface for two reasons:
- Hot water molecules at the surface evaporate, escaping into the air. Evaporation removes latent heat from the remaining water, cooling it. [1]
- The warm air directly above the water surface rises by convection, carrying thermal energy away. It is continuously replaced by cooler air, maintaining a large temperature difference that drives further heat loss. [1]
(d) Temperature drop of the open beaker in the first 6 minutes:
\[ 78 - 62 = \mathbf{16} \text{ °C} \] [1]
(e) One variable the student must control (any one): [1]
- Same volume of water in each beaker
- Same starting temperature (78 °C)
- Same type and size of beaker
- Same room temperature and conditions
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