JEE/NEET Physics · Thermodynamics series · Part 6 of 6 · All parts →
- Six parts on one card — from the first law’s receipt to time’s arrow
- ΔQ = ΔU + W · W = area under P-V · PV^γ for adiabats
- Four processes: T-slow (W=nRTlnV₂/V₁), P-rect (PΔV), V-zero, Q-zero
- η = 1 − Q_c/Q_h ≤ 1 − T_c/T_h · COP = T_c/(T_h−T_c)
- ΔS_universe ≥ 0 — the arrow nobody escapes
The final card of the Thermodynamics series — six parts on one revision sheet, plus the steam-and-silicon story of how these laws built the modern world.
- The master formula card
- The one-rule-per-part recap
- Thermodynamics in the wide world
- Final practice set
- Recap
The Master Formula Card
| What | Formula | Remember |
|---|---|---|
| First law | ΔQ = ΔU + W | in = store + spend |
| Ideal gas U | ΔU = nC_vΔT | temperature-only account |
| Work (general) | area under P-V | geometry is the answer |
| Isothermal | W = nRT ln(V₂/V₁) | Q = W exactly |
| Isobaric | W = PΔV, Q = nC_pΔT | rectangle |
| Isochoric | W = 0, Q = nC_vΔT | pure heating |
| Adiabatic | Q = 0, PV^γ = const | fast or insulated |
| Heat capacities | C_p − C_v = R | piston’s tip |
| Carnot limit | η ≤ 1 − T_c/T_h | kelvins! |
| Efficiency | η = 1 − Q_c/Q_h | always < 1 |
| Refrigerator | COP = T_c/(T_h − T_c) | reverse engine |
| Entropy | ΔS = Q/T; ΔS_univ ≥ 0 | time’s arrow |
The One-Rule-Per-Part Recap
1: in = store + spend. 2: the four moods — area under each tells the work. 3: fast means heat-free: expansion cools, compression ignites diesels. 4: sell the fall, bribe the cold — Carnot sets the ceiling. 5: mess outnumbers order; that’s why time has a direction.
Thermodynamics in the Wide World
- The Industrial Revolution WAS this chapter — Watt’s steam engine, Carnot’s analysis, diesel’s compression ignition: thermodynamics is the only physics chapter that launched an age.
- Every power station on Earth — coal, gas, nuclear, solar-thermal — is a heat engine between a hot source and a cooling tower: humanity runs on the Carnot ladder.
- Computers and data centres — Landauer’s limit links computation to entropy: information processing has a thermodynamic price; your CPU’s heat is the second law computing.
- Biology’s energy currency (ATP) — cells run microscopic heat-engine cycles (chemiosmosis): life is thermodynamics at molecular scale.
- Climate and heat death debates — Earth’s energy budget, greenhouse trapping, and the universe’s entropy destiny all run through this chapter’s laws.
Newton’s laws told us how things move; thermodynamics told us how to make movement FOR SALE. Before Carnot, engines were blacksmith guesswork; after him, machines designed on paper first. This chapter is where physics became engineering — where equations grew pistons.
Watt’s engine: ~3% efficient. Modern combined-cycle: ~60%. Two centuries of climbing Carnot’s ladder rung by rung — every rung was a material, a temperature, a pressure won from this card’s formulas. The Industrial Revolution in one number: 3 → 60.
One diagram holds the age: the P-V loop. Steam engines, car engines, jet engines, refrigerators, ACs — all are loops on this canvas, clockwise for work-out, anticlockwise for heat-pumping. Draw one loop, and you’ve drawn the machine age.
Practice set (answers hidden — try first)
(NEET-level) Q = 60 J in, W = 20 J by gas: ΔU =
(JEE Main-level) 500 K and 400 K: Carnot η =
(NEET-level) Adiabatic relation for ideal gas:
(JEE Main-level) Isothermal doubling at 2 mol, 300 K: W ≈
(NEET-level) The entropy of the universe always:
- first law receipt
- four processes and their works
- PV^γ and γ values
- Carnot ceiling + COP
- entropy’s one-way rule
- 🔁 the 12-row master card
- 🔁 one rule per part
- 🔁 thermodynamics = physics becoming engineering
- 🧠 Full-card chant: ‘receipt, moods, fast-free, ceiling, arrow’.
- 🏠 Daily: power stations = Carnot ladders at city scale.
- 🏠 Daily: your CPU’s heat is entropy computing.
Quick revision
- Six parts on one card — from the first law’s receipt to time’s arrow
- ΔQ = ΔU + W · W = area under P-V · PV^γ for adiabats
- Four processes: T-slow (W=nRTlnV₂/V₁), P-rect (PΔV), V-zero, Q-zero
- η = 1 − Q_c/Q_h ≤ 1 − T_c/T_h · COP = T_c/(T_h−T_c)
- ΔS_universe ≥ 0 — the arrow nobody escapes
- The one-rule-per-part recap
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