Irodov Part 6 Atomic and Nuclear Physics — What to Solve for JEE

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

Part Six is 310 problems of which roughly 120 are worth attempting, and only one of its seven sections — Radioactivity — is wholly on the syllabus. Two sections are off it entirely.

The pattern here is consistent and easy to hold in mind: the JEE syllabus takes the results of atomic and nuclear physics and leaves the apparatus that derives them. Bohr’s model is on it; the Rutherford scattering cross-section that motivated it is not. The de Broglie wavelength is on it; the Schrödinger equation that explains it is not. Binding energy and Q-values are on it; reaction cross sections and thresholds are not.

Apply that test and most of this part sorts itself.

Key insight. Every section in Part Six except Radioactivity opens with material the exam asks for and then keeps going into material it never will. The skill is knowing where to stop, and the test is simple: if the problem needs a cross-section, a wave function or a term symbol, it has left the syllabus.

The sections at a glance

Section 6.1 — Scattering of Particles. Rutherford–Bohr Atom

Forty-eight problems, about half in scope. The section has two halves, as its title says, and they fall on opposite sides of the syllabus.

Solve the Bohr-model half: energy levels of hydrogen-like atoms, transitions and spectral series, ionisation energies, and the scaling arguments that let you move between one-electron ions.

Skip the Rutherford scattering half: impact parameter, differential cross-section and the scattering formula are on neither syllabus.

Before you start it: Atoms.

Section 6.2 — Wave Properties of Particles. Schrödinger Equation

Forty-eight problems and only about fourteen usable. The de Broglie wavelength of matter waves is on the syllabus. The Schrödinger equation is not, and neither are particles in boxes, potential barriers or tunnelling.

Solve the de Broglie wavelength problems and the uncertainty-principle estimates as far as they are order-of-magnitude arguments. Skip everything from the Schrödinger equation onwards, which is most of the section.

Before you start it: Dual Nature of Radiation and Matter.

Section 6.3 — Properties of Atoms. Spectra

Seventy problems, the largest section in Part Six, with about twenty-five in scope. The syllabus carries characteristic and continuous X-rays and Moseley’s law, and nothing else from this section.

Solve the X-ray problems — the continuous spectrum’s short-wavelength limit, characteristic lines, Moseley’s law.

Skip multi-electron spectra, term symbols, selection rules, fine structure, the Zeeman effect and magnetic moments of atoms. That is the majority of the section, and it is university atomic physics.

Section 6.4 — Molecules and Crystals

Skip the entire section. Forty-seven problems on molecular rotation and vibration spectra, crystal lattices and the Debye theory of specific heat. None of it appears on either syllabus.

Section 6.5 — Radioactivity

Thirty-five problems, all of them in scope, and the only wholly usable section in Part Six. The law of radioactive decay, decay constant, half-life and mean life are named explicitly on the syllabus, along with alpha, beta and gamma radiation.

Irodov’s decay-chain problems — where a daughter nucleus is itself unstable — go slightly beyond what NCERT sets and are exactly the kind of thing Advanced likes, so they are worth the extra effort rather than a reason to stop.

Before you start it: Nuclei.

Section 6.6 — Nuclear Reactions

Forty-two problems, about twenty-three of them usable. Binding energy and its calculation, fission and fusion, and energy calculations in nuclear processes are all on the syllabus.

Solve the Q-value, mass-defect and binding-energy-per-nucleon problems, and the energy balance of fission and fusion. Skip reaction cross-sections, threshold energies, neutron moderation and the reactor physics at the end of the section.

Before you start it: Nuclei.

Section 6.7 — Elementary Particles

Skip the entire section. Twenty problems on conservation laws in particle decays, strangeness and particle classification. Not on either syllabus, and the last twenty problems in the book — which means a student working in order finishes on material that cannot be asked.

Common mistakes with Part Six

Treating modern physics as a small, easy chapter and doing all 310 problems. It is a small chapter in the textbook and a very large part of Irodov, most of which is university material. The ratio here is among the worst in the book.

Doing 6.1 from the front. The Rutherford scattering material opens the section, so a student working in order meets the unusable half first and often concludes the whole section is beyond them. Start with the Bohr problems.

Skipping 6.5 because radioactivity looks like formula substitution. It is the only fully in-scope section in the part, and its decay-chain problems are genuinely demanding.

Confusing binding energy with cross-sections in 6.6. Both are “nuclear reactions”. One is on the syllabus and one has never been.

What to read next

• Part 1 — Mechanics, the best value in the book
• Part 5 — Optics
• Should you solve Irodov at all?