Quick questions on Thermodynamics and heat transfer: VCE Physics Unit 1 Year 11

Heat flow through a material by particle vibration and collision. Solids conduct best; gases conduct poorly. Metals are excellent conductors due to free electrons.

Heat transfer by bulk movement of a fluid (liquid or gas). Hot fluid is less dense, rises; cold fluid sinks. Drives weather, ocean currents, the slow circulation of the Earth's mantle.

Heat transfer by electromagnetic waves (infrared mainly). Does not require a medium. Stefan-Boltzmann law: $P = \sigma A T^4$ where $\sigma = 5.67 \times 10^{-8}$ W m$^{-2}$ K$^{-4}$, $A$ surface area, $T$ absolute temperature.

Earth absorbs sunlight ($\sim 1370$ W/m$^2$ at the top of atmosphere, with about 30% reflected). The absorbed energy is re-emitted as infrared. Greenhouse gases absorb some of this infrared and re-radiate it (some down to the surface, some up).

Without it, Earth's surface would average about -18 degrees C. With it, about +15 degrees C. Life as we know it depends on the natural greenhouse effect.

Human activities (fossil fuel burning, deforestation, agriculture) have increased atmospheric CO2 from approximately 280 ppm (pre-industrial) to over 420 ppm (2024). The enhanced greenhouse effect drives observed climate change.

A doubling of CO2 from pre-industrial values is estimated to produce 2.5 to 4 degrees C of warming at equilibrium.

A bath of cool water can have more total internal energy than a hot cup of tea.

For some thermodynamics formulas, absolute temperature (Kelvin) is required (Stefan-Boltzmann, gas laws). For $\Delta T$, either scale works because differences are the same.

Different materials have very different values. Use the value for the correct substance.

During melting or boiling, temperature does not change but energy is absorbed. Include the latent heat term.

Different phenomena. The greenhouse effect is about heat trapping. Ozone depletion is about UV transmission through the upper atmosphere.