Two identical metal flasks, X and Y, are filled with equal volumes of hot water at 90∘C90^\circ\text{C}90∘C and left to cool in a draft-free room at 20∘C20^\circ\text{C}20∘C. The outer surface of flask X is painted dull black, and the outer surface of flask Y is polished silver.
How and why would the temperature readings of the water in the two flasks differ after a short period of time?
X would have a lower temperature than Y because black is a good emitter of radiation.
X would have a lower temperature than Y because black is a poor emitter of radiation.
X would have a higher temperature than Y because black is a good emitter of radiation.
X would have a higher temperature than Y because black is a poor emitter of radiation.
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.