A student investigates the transfer of thermal energy from a beaker containing 150 cm3150\text{ cm}^3150 cm3 of hot water. Under identical initial conditions, the experiment is conducted twice: once with an open beaker A (without a lid) and once with a beaker B (fitted with a lid).
The temperature θ\thetaθ is recorded every 40 s40\text{ s}40 s up to 240 s240\text{ s}240 s. The results are shown in Table 1.1.
Table 1.1
| t/st / \text{s}t/s | θA/∘C\theta_A / ^\circ\text{C}θA/∘C | θB/∘C\theta_B / ^\circ\text{C}θB/∘C |
|---|---|---|
| 0 | 85.0 | 85.0 |
| 40 | 81.5 | 83.5 |
| 80 | 78.5 | 82.0 |
| 120 | 76.0 | 80.8 |
| 160 | 74.0 | 79.7 |
| 200 | 72.3 | 78.8 |
| 240 | 71.0 | 79.0 |
Write a conclusion stating how using the lid affects the cooling of the water.
Calculate the average rate of change of temperature xAx_AxA of the water in beaker A. Use the values from Table 1.1 and the equation:
xA=θ0−θ240T x_A = \frac{\theta_0 - \theta_{240}}{T} xA=Tθ0−θ240where θ0\theta_0θ0 is the temperature at t=0t = 0t=0, θ240\theta_{240}θ240 is the temperature at t=240 st = 240\text{ s}t=240 s, and T=240 sT = 240\text{ s}T=240 s. Include the unit.
Calculate the average rate of change of temperature xBx_BxB of the water in beaker B. Use the values from Table 1.1 and the equation:
xB=θ0−θ240T x_B = \frac{\theta_0 - \theta_{240}}{T} xB=Tθ0−θ240where θ0\theta_0θ0 is the temperature at t=0t = 0t=0, θ240\theta_{240}θ240 is the temperature at t=240 st = 240\text{ s}t=240 s, and T=240 sT = 240\text{ s}T=240 s. Include the unit.
Thermal energy is transferred both from the surface of the water and from the sides of the beaker. A student suggests that more thermal energy is transferred from the surface of the water than from the sides of the beaker.
State whether the results support this suggestion. Justify your statement by reference to your values of xAx_AxA and xBx_BxB.
Suggest a change to the apparatus or the procedure to produce a greater difference between xAx_AxA and xBx_BxB.
301 exam-style questions on CIE IGCSE Physics 2.3 Transfer of thermal energy, covering 2.3.1a Thermal conductors and thermal insulators, 2.3.1b Explaining thermal conduction, 2.3.2 Convection, 2.3.3a Thermal radiation, 2.3.3b Surface colour and texture, 2.3.3c Rate of emission and absorption of radiation, and 2.3.4 Consequences of thermal energy transfer. Each one has a worked solution and a mark scheme showing where the marks go.