A student is investigating how partly covering the surface of the water in a beaker affects the rate at which the water cools.
The apparatus used is shown in Fig. 1.1.
Record the room temperature θR, in °C, shown on the thermometer in Fig. 1.2.
θR = .........................................................
The student pours 100 cm3 of hot water into a beaker. She places lid A on the beaker. This leaves half of the water surface uncovered, as shown in Fig. 1.3.
She records the temperature of the water in the beaker and immediately starts a stopclock.
She records the temperature θ of the water every 30 s. Her readings are shown in Table 1.1.
She repeats the procedure using lid B. This leaves a quarter of the water surface uncovered, as shown in Fig. 1.4.
Complete the headings and the time t column in Table 1.1.
Table 1.1
beaker with lid A | beaker with lid B | |
t / | θ / | θ / |
0 | 80.0 | 81.0 |
77.0 | 79.0 | |
74.5 | 77.5 | |
72.5 | 76.0 | |
70.5 | 75.0 | |
69.5 | 74.0 | |
68.0 | 73.5 |
Describe a precaution that should be taken to ensure that the temperature readings are as accurate as possible in the experiment.
(i) Write a conclusion to this experiment, stating for which lid the rate of cooling is greater.
Explain your answer by reference to the results.
[2]
(ii) Suggest a change to the apparatus that could produce a greater difference between the rates of cooling for lid A and lid B.
Explain why the change might produce a greater difference.
[2]
A student suggests that the rate of cooling is directly proportional to the percentage of the uncovered surface area. He wants to draw a graph of cooling rate against the percentage of uncovered area to investigate this.
Describe how his graph line will show whether the rate of cooling and the percentage of uncovered surface area are directly proportional.
Students in other countries carry out the same experiment.
Suggest one factor that they should keep the same if they are to obtain similar readings.
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