Define the internal energy of a substance.
A sample of liquid sulfur is solidifying at a constant temperature of 115∘C115^\circ\text{C}115∘C. Use the behaviour of the sulfur molecules to describe and explain the changes to the internal energy of the sulfur 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.