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.
99 exam-style questions on CIE IGCSE Physics 2.3.3a Thermal radiation. Each one has a worked solution and a mark scheme showing where the marks go.