Thermal physics and the kinetic model
Thermal physics and the kinetic model tests temperature, heat transfer, specific heat capacity and particle explanations.
Core ideas
- Temperature measures average kinetic energy of particles; thermal energy transfer occurs from hotter to cooler regions.
- Conduction: particle vibrations and free electrons transfer energy, mainly in solids. Convection: density changes drive fluid circulation. Radiation: infrared electromagnetic waves; no medium needed; dark matt surfaces absorb/emit better.
- Specific heat capacity c is energy needed to raise 1 kg by 1°C: E = mcΔT. Unit J/(kg°C).
- Latent heat is energy for state change at constant temperature; E = mL.
- Gas pressure results from particle collisions with walls; increasing temperature increases pressure at constant volume.
Worked example
Heat 2.0 kg of water from 20°C to 50°C. ΔT=30°C. E = mcΔT = 2.0×4200×30 = 252000 J = 252 kJ. If a 500 W heater supplies this, time = E/P = 252000/500 = 504 s, about 8.4 minutes, ignoring losses. During boiling, temperature stays at 100°C while latent heat converts liquid to gas.
Traps
Forgetting that gas-law calculations need kelvin; forgetting mass in kg; confusing specific heat capacity with latent heat; saying heat rises instead of explaining convection; ignoring energy losses.