A student investigates how the temperature of the surroundings affects the rate of cooling of water. Start with approximately 100 cm³ of hot water in a 250 cm³ beaker. The initial thermometer reading is shown in Fig. 2.1.
Table 2.1 gives time t / s and temperature θ / °C: (0, your Fig. 2.1 reading), (30, 69), (60, 67), (90, 66), (120, 65), (150, 64), (180, 63), (210, 62), (240, 61).
(a)(i)Record the initial temperature in Table 2.1.
(a)(ii)Explain why the water is carefully stirred before each temperature reading.
(a)(iii)Calculate average cooling rate C₁ during the first 90 s, using C₁ = (θ₀ − θ₉₀)/90. Give the unit.
(a)(iv)Calculate average cooling rate C₂ during the final 90 s, using C₂ = (θ₁₅₀ − θ₂₄₀)/90. Give the unit.
(a)(v)Compare C₁ and C₂ and explain any difference.
Repeat with 100 cm³ of hot water in the smaller beaker placed carefully inside a larger beaker containing 100 cm³ of iced water. Do not mix the water between beakers. The arrangement is shown in Fig. 2.2.
Table 2.2 gives time t / s and temperature θ / °C: (0, 75), (30, 68), (60, 62), (90, 57).
(b)(i)Calculate C₃ = (θ₀ − θ₉₀)/90 for the first 90 s. Give the unit.
(b)(ii)Describe how C₃ differs from C₁. Explain your answer.
(b)(iii)By referring to the results in both tables, explain why this experiment is not a valid comparison of C₁ and C₃.
(b)(iv)State one other variable that should be kept constant for a valid comparison.
5054/41/M/J/24Cambridge O Level Physics 5054 · May/June 2024 · Paper 4 variant 1 · Question 2