Irodov Part 2 Thermodynamics — Which Problems to Solve for JEE

A section-by-section map of Part Two of I.E. Irodov’s Problems in General Physics, checked against the JEE Main and JEE Advanced syllabuses.

Part Two is the weakest part of Irodov for a JEE candidate, and it is worth knowing that before you commit an evening to it. Of 257 problems, only 86 sit in sections that are wholly in scope and roughly 133 are worth attempting at all. The reason is structural: Irodov is a Russian university text, and Russian university thermodynamics goes straight into statistical mechanics — the Maxwell speed distribution, the Boltzmann factor, entropy as a calculated quantity — none of which the JEE syllabus carries.

What remains is good. Irodov’s gas-process problems demand that you track a thermodynamic path rather than plug into a formula, which is the exact skill Advanced tests when it gives you a graph and asks for the heat absorbed.

Key insight. In this part, the question to ask of every problem is whether it needs a distribution or only a state. If it mentions a fraction of molecules, a most probable speed, or entropy change, it has left the syllabus. If it asks about pressure, temperature, work or heat along a path, it is yours.

The sections at a glance

Section 2.1 — Equation of the Gas State. Processes

Twenty-five problems, all usable. Ideal gas laws, mixtures, and processes defined by a relation between pressure and volume rather than by a name. That last habit is the valuable one: Irodov will give you $pV^n = \text{constant}$ for some $n$ you have not met and expect you to work out the heat capacity of that process yourself.

Before you start it: Kinetic Theory.

Section 2.2 — The First Law of Thermodynamics. Heat Capacity

Thirty-six problems, all in scope. The first law applied to ideal gases, molar heat capacities for monoatomic and diatomic gases, isothermal and adiabatic processes. This is the strongest section in Part Two and the one to do if you do only one.

Before you start it: Thermodynamics.

Section 2.3 — Kinetic Theory. Boltzmann’s Law and Maxwell’s Distribution

Fifty-one problems, of which perhaps eighteen survive. The syllabus carries the kinetic interpretation of temperature, degrees of freedom, equipartition and mean free path. It does not carry the Maxwell speed distribution or the Boltzmann barometric formula, and those are the majority of this section.

Solve the problems on molecular speeds as averages, equipartition, degrees of freedom and mean free path. Skip anything that integrates a distribution function, asks for the fraction of molecules in a speed range, or uses the barometric formula.

Section 2.4 — The Second Law of Thermodynamics. Entropy

Forty-seven problems, and this section divides sharply by which exam you are sitting. The second law, reversible and irreversible processes and Carnot efficiency are all on the JEE Advanced syllabus. The Carnot engine and its efficiency are not on the JEE Main syllabus at all.

So: if you are targeting Advanced, roughly nineteen problems here are worth doing — the cycle and efficiency ones. If you are sitting Main only, skip the section outright. Entropy calculations are outside both syllabuses regardless.

Section 2.5 — Liquids. Capillary Effects

Twenty-five problems, all in scope. Surface energy, surface tension, angle of contact and capillary rise are named explicitly on the syllabus, and Irodov’s treatment of excess pressure across curved surfaces is unusually clear.

Before you start it: Mechanical Properties of Fluids.

Section 2.6 — Phase Transformations

Skip the entire section. Thirty-five problems built on the Clausius–Clapeyron equation, which is on neither syllabus. A few latent-heat problems are technically answerable, but not enough to justify opening the section to hunt for them.

Section 2.7 — Transport Phenomena

Thirty-eight problems, of which about ten are usable. The syllabus carries one-dimensional heat conduction and Newton’s law of cooling — though Newton’s law of cooling is not on the JEE Main syllabus — so the conduction problems are worth doing if Advanced is the target.

Solve steady-state conduction through slabs, rods and composite walls. Skip everything derived from kinetic theory: diffusion coefficients, the viscosity of gases, and thermal conductivity computed from mean free path.

Before you start it: Thermal Properties of Matter.

Common mistakes with Part Two

Doing 2.3 in full because kinetic theory is on the syllabus. It is; Maxwell’s distribution is not. Two-thirds of that section is university statistical mechanics wearing a familiar chapter name, and it is the commonest place in the book to lose a week to nothing.

Assuming the Carnot problems are safe because they are famous. They are safe for Advanced and worthless for Main since 2024. This is the sharpest Main-versus-Advanced split anywhere in Irodov.

Skipping 2.5 because surface tension feels like a small topic. It is a small topic with twenty-five fully usable problems and a reliable presence in the papers — among the best problems-per-hour in the book.

Treating entropy problems as hard thermodynamics worth attempting. They are not hard for the syllabus; they are outside it. Working them builds nothing you can be examined on.

What to read next

• Part 1 — Mechanics, the strongest part for JEE
• Part 3 — Electrodynamics
• Should you solve Irodov at all?