Define the internal energy of a substance.
A sample of molten lead is solidifying into solid lead at a constant temperature of 327∘C327^\circ\text{C}327∘C. Use the behaviour of the lead atoms to describe and explain the changes to the internal energy of the lead as it solidifies.
56 exam-style questions on OCR A A Level Physics Thermal physics, covering Temperature, Solid, liquid and gas, Thermal properties of materials, and Ideal gases. Each one has a worked solution and a mark scheme showing where the marks go.