Question EXE.2.SL.TZ0.3
| Date | Example questions Example questions | Marks available | [Maximum mark: 8] | Reference code | EXE.2.SL.TZ0.3 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Comment, Describe | Question number | 3 | Adapted from | N/A |
A steel pot containing water is placed on an electric hot plate that is preheated to a temperature of 180 °C. The initial temperature of the water in the pot is 10 °C.
The base of the pot has a surface area of 0.15 m2 and a thickness of 5.0 mm. The coefficient of thermal conductivity of the material of the pot is 45 W m−1 K−1.
Calculate:
the initial temperature gradient through the base of the pot. State an appropriate unit for your answer.
[2]
✓
K m−1 ✓
the initial rate, in kW, of thermal energy transfer by conduction through the base of the pot.
[1]
45 × 0.15 × 3.4 × 104 = 230 «kW» ✓
The electrical power rating of the hot plate is 1 kW. Comment, with reference to this value, on your answer in (a)(ii).
[3]
The answer is unrealistically large / impossible to sustain ✓
Due to much lower actual power, a lower temperature gradient through the base of the pot is quickly established ✓
The surface of the hot plate becomes colder from contact with pot
OR
there is a temperature gradient also through the hot plate ✓
Describe how thermal energy is distributed throughout the volume of the water in the pot.
[2]
By means of convection currents ✓
That arise due to density difference between hot and cold water ✓