A substance cools from 80∘C80^\circ\text{C}80∘C to 10.0∘C10.0^\circ\text{C}10.0∘C. Its melting point is 40∘C40^\circ\text{C}40∘C. The substance takes 20 minutes to cool from 80∘C80^\circ\text{C}80∘C to its melting point.
The substance takes a total time of 90 minutes to cool from 80∘C80^\circ\text{C}80∘C to 10.0∘C10.0^\circ\text{C}10.0∘C.
Describe the key features of the temperature-time cooling curve from t=0 mint = 0\text{ min}t=0 min to t=90 mint = 90\text{ min}t=90 min, specifying the coordinates of key points, the shape of the sections, and what process is occurring during the period of constant temperature.
Describe the arrangement and motion of the molecules in this substance when they are in the liquid state.
313 exam-style questions on CIE IGCSE Physics 2.2.3a Melting, boiling, condensation and solidification. Each one has a worked solution and a mark scheme showing where the marks go.