The diagram shows the temperature-time graph for hot water that is cooling in an insulated beaker. The curve starts at 80∘C80^\circ\text{C}80∘C at 0 hours0\text{ hours}0 hours, decreases gradually, and levels off to a horizontal line at 20∘C20^\circ\text{C}20∘C at about 2.5 hours2.5\text{ hours}2.5 hours.
The insulation is now removed from the beaker. The same volume of hot water, at the same initial temperature of 80∘C80^\circ\text{C}80∘C, is put into the uninsulated beaker in the same room as before.
Which of the following describes the new temperature-time graph for the water as it cools?
The curve falls more steeply than the original and levels off at 20∘C20^\circ\text{C}20∘C.
The curve falls less steeply than the original and levels off at 20∘C20^\circ\text{C}20∘C.
The curve falls more steeply than the original and levels off at 40∘C40^\circ\text{C}40∘C.
The curve falls less steeply than the original and levels off at 40∘C40^\circ\text{C}40∘C.
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.