Physics (university) · Part 06
Thermodynamics
Temperature, heat, gases, and the laws that limit engines.
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- TemperatureA measure of the average kinetic energy of the particles in something. The SI scale is kelvin: K = degrees Celsius + 273.15.
- Thermal expansionMost solids lengthen when heated by an amount change in L = alpha x L x change in T.
- Specific heatThe energy needed to raise 1 kg of a material by 1 K. Heat Q = m c change in T.
- Latent heatEnergy absorbed or released when a substance changes state without changing temperature. Q = m L.
- Heat transferHeat moves by conduction (through touching matter), convection (moving fluid) and radiation (electromagnetic waves).
- Ideal gas lawFor a gas, PV = nRT, with pressure in pascals, volume in cubic metres and temperature in kelvin. R is 8.314 J/(mol K).
- Kinetic theoryGas pressure comes from molecules hitting the walls. The average kinetic energy of a molecule is 3/2 k T.
- First law of thermodynamicsChange in internal energy equals heat added minus work done by the system: change in U = Q - W. It is energy conservation.
- Heat enginesA machine that turns heat into work. Efficiency is work out over heat in. Carnot's limit is 1 - Tc/Th.
- EntropyA measure of disorder, or how many ways energy can be spread out. In an isolated system it never decreases.