A student investigates the rate of cooling of water at the top and at the bottom of a beaker of hot water. (a) The student: • measures the room temperature θR as θR = 22.5 °C • pours 200 cm³ of hot water into a beaker • lowers a thermometer into the beaker until its bulb is just covered by the hot water, as shown in Fig. 2.1 • waits for approximately 30s • starts a stop-watch and reads the thermometer.

1. (a)(i)The temperature on the thermometer at time t = 0 is shown in Fig. 2.2. Record the temperature reading at time t = 0 to the nearest 0.5°C in Table 2.1. [1][1]
2. (a)(ii)Explain why the student waits for 30s before reading the initial temperature of the hot water. [1][1]
3. (b)(i)The student waits for 3 minutes, reads the thermometer and records the new temperature reading in Table 2.1. The student then: • removes the thermometer from the beaker and pours the water away • repeats the procedure in (a), but lowers the thermometer into the beaker, so that the bulb is just above, but not touching the bottom of the beaker, as shown in Fig. 2.3. • records the initial and final temperatures of the water as shown in Table 2.1. Calculate the average rate of cooling P_T of the hot water at the top of the beaker. Use the equation: average rate of cooling = decrease in temperature of the water / time taken Give your answer to 2 significant figures and state the unit. P_T= .............................................. unit .............................. [3][3]
4. (b)(ii)Use the data in Table 2.1 on page 7 to calculate the average rate of cooling P_B of the hot water at the bottom of the beaker. P_B = .............................................. [1][1]
5. (c)(i)Use your answers to (b)(i) and (b)(ii) to suggest why a hot liquid should be stirred before measuring its temperature. [1][1]
6. (c)(ii)State one way in which the apparatus in this experiment is arranged to make it easy to read the thermometer accurately. [1][1]
7. (d)The experiment is repeated to check the results. Suggest one variable that must be kept constant. [1][1]
8. (e)The student leaves the thermometer in the hot water and waits for 30 minutes before reading the thermometer again. Predict a value for the temperature of the water in the beaker. temperature of water = .............................................. °C [1][1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.