π₯ THERMODYNAMICS Β· Laws & Engines
Zeroth Law β’ First Law β’ Second Law β’ Carnot Engine β’ Entropy β’ NEET problems
π LAWS OF THERMODYNAMICS
Zeroth Law
If two systems are in thermal equilibrium with a third, they are in equilibrium with each other. Basis of temperature measurement.
First Law (Energy Conservation)
ΞU = Q β W
Change in internal energy = heat added β work done by system.
For infinitesimal: dU = dQ β dW
Second Law (Entropy)
KelvinβPlanck: No engine can convert all heat into work.
Clausius: Heat cannot flow spontaneously from cold to hot.
Entropy of isolated system never decreases: ΞS β₯ 0.
Third Law
As T β 0, entropy β 0 (perfect crystal).
βοΈ THERMODYNAMIC PROCESSES
Isothermal (T constant): ΞU = 0 β Q = W. W = nRT ln(Vβ/Vβ)
Adiabatic (Q = 0): ΞU = βW. PVΞ³ = constant, TVΞ³β1 = constant. W = (PβVβ β PβVβ)/(Ξ³β1)
Isobaric (P constant): W = PΞV, Q = nCpΞT
Isochoric (V constant): W = 0, Q = ΞU = nCvΞT
π PV diagrams for processes
π CARNOT ENGINE (Ideal Heat Engine)
Most efficient engine operating between two temperatures Tβ (hot) and Tβ (cold). Cycle: isothermal expansion β adiabatic expansion β isothermal compression β adiabatic compression.
Efficiency: Ξ· = 1 β Tβ/Tβ = 1 β Qβ/Qβ (maximum possible).
Work done: W = Qβ β Qβ
π Carnot cycle on PV diagram
βοΈ HEAT ENGINES & REFRIGERATORS
Heat engine: Ξ· = W/Qβ = 1 β Qβ/Qβ
Refrigerator: COP = Qβ/W = Qβ/(QββQβ)
Heat pump: COP = Qβ/W = Qβ/(QββQβ)
For Carnot refrigerator: COPmax = Tβ/(TββTβ)
π ENTROPY & SECOND LAW
Entropy (S): Measure of disorder. ΞS = β« dQrev/T (reversible path).
For reversible process, ΞStotal = 0; for irreversible, ΞStotal > 0.
Entropy change in:
β’ Isothermal expansion: ΞS = nR ln(Vβ/Vβ)
β’ Phase change: ΞS = mL/T
β’ Heating: ΞS = nC ln(Tβ/Tβ)
π‘ NEET TIPS & SHORTCUTS
- For isothermal process, ΞU = 0, Q = W.
- For adiabatic process, Q = 0, ΞU = βW.
- In cyclic process, net work = area enclosed in PV diagram.
- Cp β Cv = R for ideal gases. Ξ³ = Cp/Cv = 1 + 2/f (f = degrees of freedom).
- For monatomic gas: f = 3, Ξ³ = 5/3; diatomic: f = 5, Ξ³ = 7/5; polyatomic: f = 6, Ξ³ = 4/3.
β οΈ COMMON MISTAKES
- Using Cv for isobaric process instead of Cp.
- Forgetting sign convention in First Law: ΞU = Q β W (work done BY system).
- Assuming adiabatic process means constant temperature β it's constant heat.
- Applying Carnot efficiency formula without converting temperatures to Kelvin.
π QUICK REVISION CARD
First law: ΞU = Q β W
Isothermal work: W = nRT ln(Vβ/Vβ)
Adiabatic work: W = (PβVβ β PβVβ)/(Ξ³β1)
Efficiency (Carnot): Ξ· = 1 β Tβ/Tβ
Cp β Cv = R
Ξ³ = Cp/Cv
π₯ THERMODYNAMICS β’ NEET REVISION NOTES
πΈ NOTES PREVIEW
Preview of Thermodynamics Notes
π₯ DOWNLOAD THERMODYNAMICS NOTES PDF
Download Thermodynamics Revision Notes for NEET Physics PDF for fast revision and strong conceptual clarity. This chapter is one of the most important and high-weightage topics in NEET Physics.
These Thermodynamics handwritten notes PDF free download include laws of thermodynamics, heat engine, entropy, Carnot cycle, and all important formulas, tricks, and PYQ-based concepts.
- High probability of questions in NEET
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- Entropy and Carnot cycle frequently asked
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π WEIGHTAGE ANALYSIS
2β3 Questions
Laws + heat engine + entropy
High Weightage
Theory + derivations + numericals
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