Quick questions on Thermal physics and kinetic theory: QCE Physics Unit 1 Year 11

Energy flows through a material by particle vibration and collision, passing kinetic energy from hot particles to neighbouring cooler ones. Solids conduct best because their particles are close-packed; metals are exceptional conductors because free (delocalised) electrons carry energy rapidly through the lattice. Gases conduct poorly, which is why trapped air is a good insulator.

Heat is carried by the bulk movement of a fluid (liquid or gas). When a fluid is heated it expands, becomes less dense and rises, while cooler denser fluid sinks to replace it, setting up a convection current. Convection drives sea breezes, ocean currents and the circulation in a heated room, and it cannot occur in a solid.

Energy is transferred by electromagnetic waves (predominantly infrared) and, uniquely, requires no medium, so it crosses a vacuum. Every object above $0\ \text{K}$ radiates. The Stefan-Boltzmann law gives the power radiated:

State the kinetic theory definition of temperature. [2 marks]

A $0.40 \text{ kg}$ aluminium block ($c = 900 \text{ J kg}^{-1} \text{ K}^{-1}$) absorbs $7200 \text{ J}$. Calculate the temperature rise. [2 marks]

Identify and analyse the three heat-transfer mechanisms in a Queensland slate-roofed home in summer. (a) Describe each mechanism in context. (b) Calculate the radiative loss from a $30 \text{ m}^2$ roof at $60^\circ \text{C}$ to a sky at $20^\circ \text{C}$ (emissivity $0.9$, $\sigma = 5.67 \times 10^{-8} \text{ W m}^{-2} \text{ K}^{-4}$).