Adiabatic = no heat exchange, Q - W Ex. Free (adiabatic) expansion. ∆U= = Cp/Cv , TVγ-1 = constant, pVγ = constant. γ W = 0 Isochoric = constant volume Isothermal = constant temperature if ideal gas, U is proportional to T (not p or V), = 0 and Q = W. ∆U For an ideal gas, Cp (constant pressure) = Cv (constant volume)+ R. 20. The Second Law of Thermodynamics. The Second Law (4 versions): 1. Heat flows spontaneously from hot to cold, not the other way around. Clausius. The efficiency of a heat 2. Heat cannot be converted completely into work. engine or refrigerator is never = 100%. Efficiency, e = W/QH = 1 |QC/QH| And – 2nd Law is that e never reaches 1. Otto (automobile) = 1 1/rγ-1, where r is the compression ratio (Volume – ratio—max to min). Carnot Cycle (most efficient) e = 1 - TC/TH. Must be Kelvin temperature. 3. Entropy (∆S = Q/T at a constant temperature) always increases for a macroscopic closed system). = This is the same for all processes ∆S≥0. ∆S ∫dQ/T. leading between two states. Thus we can choose a process which is easy to calculate (like isothermal, T =const.). 4. Information: S =k ln w, w is the number of microscopic states.
Adiabatic = no heat exchange, Q ∆U= - W Ex. Free (adiabatic) expansion. γ = Cp/Cv , TVγ-1 = constant, pVγ = constant. Isochoric = constant volume W = 0 Isothermal = constant temperature if ideal gas, U is proportional to T (not p or V), ∆U = 0 and Q = W. For an ideal gas, Cp (constant pressure) = Cv (constant volume)+ R. 20. The Second Law of Thermodynamics. The Second Law (4 versions): 1. Heat flows spontaneously from hot to cold, not the other way around. Clausius. 2. Heat cannot be converted completely into work. The efficiency of a heat engine or refrigerator is never = 100%. Efficiency, e = W/QH = 1 – |QC/QH| And 2nd Law is that e never reaches 1. Otto (automobile) = 1 – 1/rγ-1, where r is the compression ratio (Volume ratio—max to min). Carnot Cycle (most efficient) e = 1 - TC/TH. Must be Kelvin temperature. 3. Entropy (∆S = Q/T at a constant temperature) always increases for a macroscopic closed system). ∆S≥0. ∆S = ∫dQ/T. This is the same for all processes leading between two states. Thus we can choose a process which is easy to calculate (like isothermal, T =const.). 4. Information: S =k ln w, w is the number of microscopic states.
P8%20Desert%20Island%20Physics.docx