What the board asks
We went through the ISC board papers, question by question, and matched each question to a topic. Here is what was asked, how often, and what was never asked.
Physics: 427 topics in the 2027 syllabus, across 9 units. The board has asked 269 of them at least once. 158 were never asked in the papers we checked.
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P8 Atoms and Nuclei
All the topics in Physics: Atoms and Nuclei
Asked topics first, the most asked at the top. Tap a topic to see what to write, the result, the years, and the real board questions.
38 topics shown
| # | Topic | Type | Marks | Times asked | Last asked | Status |
|---|---|---|---|---|---|---|
| 1 | State Bohr's postulates for the hydrogen atomState the three postulates with their equations (electron moves in stationary circular orbits without radiating, the Coulomb force supplying the centripetal force; only orbits with angular momentum an integral multiple of h/(2 pi) are allowed; a photon of energy h f = E2 - E1 is emitted or absorbed when the electron jumps between two orbits) and explain in one line what 'angular momentum is quantised' means. | Statement | 2 | 7 papers | Specimen 2027 | Asked |
| 2 | Numericals: scaling of r, v, E and L with nGiven the value for the first orbit (r0, v0 or -13.6 eV), write the value for the nth orbit and ratios between two orbits using r proportional to n^2, v proportional to 1/n, E proportional to 1/n^2 and L = n h/(2 pi); also find KE and PE from a given total energy. | Numericals | 1 | 5 papers | 2026 | Asked |
| 3 | Nuclear reactor: main parts, their functions, useName the five main parts of a nuclear reactor (fuel elements, moderator, control rods, coolant, casing), give one material and the function of each, state how the reactor is kept critical and how it is shut down in an emergency (control rods pushed fully in), and describe how the energy output is used (heat to steam to turbine to electricity). | Device | 3 | 5 papers | 2025 | Asked |
| 4 | Hydrogen spectrum: five series, wavelength formulae, regionsWrite the general wavelength formula, then for the Lyman, Balmer, Paschen, Brackett and Pfund series give the lower level, the values the upper level can take, the formula for that series and the region of the spectrum it lies in, and state the value of the Rydberg constant. | Statement | 1 | 4 papers | Specimen 2027 | Asked |
| 5 | Numericals: threshold energy for pair production, annihilation energyCompute the minimum energy a gamma ray photon needs to create a particle-antiparticle pair as 2 m c^2, in joule and in MeV, for an electron-positron pair and for a proton-antiproton pair; also the kinetic energy shared by the pair when the photon has more than this, and the energy of each photon produced in annihilation. | Numericals | 2 | 3 papers | Specimen 2027 | Asked |
| 6 | Energy level diagram of hydrogen with series transitionsDraw horizontal levels for n = 1 to 5 and n = infinity with their energies marked, the gaps shrinking upward, and show with arrows the transitions that give the Lyman, Balmer, Paschen, Brackett and Pfund series (downward arrows for emission lines, upward arrows for absorption lines), naming each series. | Diagram | 3 | 3 papers | 2025 improvement | Asked |
| 7 | Mass defect, binding energy, binding energy per nucleon: definitionsDefine mass defect with its formula, binding energy of a nucleus and binding energy per nucleon, and state the physical significance of binding energy per nucleon (it measures how tightly each nucleon is held, so the stability of the nucleus). | Statement | 2 | 3 papers | 2025 | Asked |
| 8 | Nuclear fusion: definition, equation, conditions, where it occursDefine nuclear fusion (two or more light nuclei combine to form a heavier nucleus with release of energy), write the equation for four hydrogen nuclei forming helium, state the very high temperature it needs, and name where it occurs (the Sun and stars; the hydrogen bomb). | Statement | 1 | 3 papers | 2025 | Asked |
| 9 | Pair production and pair annihilation with balanced equationsDefine pair production (a gamma ray photon of enough energy, passing close to a heavy nucleus, changes into an electron and a positron) and pair annihilation (an electron and a positron meet and their mass is converted into two gamma ray photons), write a balanced equation for each, and state the minimum photon energy for electron-positron pair production. | Statement | 2 | 3 papers | 2024 | Asked |
| 10 | Derive orbital velocity of the electron in nth orbitWrite the equation of circular motion and the angular momentum condition, divide one by the other to eliminate r, obtain v_n, and show that v_n is inversely proportional to n. | Derivation | 3 | 2 papers | Specimen 2027 | Asked |
| 11 | Isotopes, isobars and isotones: definitions with examplesDraw a three-row table giving for isotopes, isobars and isotones what is the same, what differs, and two examples each written in nuclide notation. | Comparison | 1 | 2 papers | Specimen 2027 | Asked |
| 12 | Numericals: wavelength of a spectral line (Rydberg formula)Using 1/lambda = R (1/n1^2 - 1/n2^2), compute the shortest wavelength (series limit, n2 = infinity) and the longest wavelength (first line, n2 = n1 + 1) of a named series, and the wavelength of any stated transition, giving the answer in nm. | Numericals | 2 | 2 papers | 2026 | Asked |
| 13 | Bohr model reasoning: negative energy, ionisation, excitationAnswer in one or two lines each: what the negative total energy of the orbiting electron signifies; why the energy rises towards zero as n increases while the levels crowd together; what the ionisation energy and first excitation energy of hydrogen are, read from the level energies; and why an electron in a stationary orbit does not radiate in Bohr's model. | Give reason | 1 | 2 papers | 2026 | Asked |
| 14 | Graph: binding energy per nucleon versus mass numberDraw the labelled curve of BE per nucleon (MeV) against mass number A: steep rise for light nuclei with small peaks at 4He, 12C and 16O, a broad maximum of about 8.75 MeV near A = 56 (iron), then a slow fall to about 7.6 MeV near A = 240; mark the most stable nucleus and list the special features. | Graph | 2 | 2 papers | 2026 | Asked |
| 15 | Derive radius of the nth Bohr orbitWrite the centripetal force equation and the quantisation condition, eliminate v between them to obtain r_n, show that r_n is proportional to n^2, and state the radius of the first orbit. | Derivation | 3 | 2 papers | 2025 | Asked |
| 16 | Nuclear fission: definition and one balanced equationDefine nuclear fission (a heavy nucleus, struck by a slow neutron, splits into two nuclei of comparable mass with the release of neutrons and a large amount of energy) and write one balanced fission equation with mass numbers and atomic numbers shown. | Statement | 1 | 2 papers | 2025 improvement | Asked |
| 17 | Numericals: mass defect and binding energy of a nucleusFrom the given masses of the proton (or hydrogen atom), the neutron and the nucleus (or atom), compute the mass defect in u, the binding energy in MeV using the given value of 1 u, and the binding energy per nucleon. | Numericals | 2 | 2 papers | 2024 | Asked |
| 18 | Show nuclear density is independent of mass numberTake the nucleus as a sphere of radius R = R0 A^(1/3), write its mass as m A (m = average mass of a nucleon), divide by the volume (4/3) pi R^3, show that A cancels, and state the value and what it means (all nuclei have the same, enormous density). | Derivation | 2 | 1 paper | Specimen 2027 | Asked |
| 19 | Mass-energy relation: prove 1 u = 931.5 MeVState Einstein's mass-energy relation, substitute m = 1 u in kg and c, get the energy in joule, convert to eV and then MeV; in the same way find the energy equivalent of any given mass (1 g, 1 kg, the electron rest mass). | Numericals | 2 | 1 paper | Specimen 2027 | Asked |
| 20 | Fusion reasoning: why thermonuclear, why hard to achieveExplain in two lines each: why fusion needs a very high temperature (nuclei are positively charged and must have enough kinetic energy to overcome their electrostatic repulsion and come close enough to fuse) and so is called a thermonuclear reaction; why it is difficult to achieve and control on Earth; and why the Sun and stars can sustain it. | Give reason | 1 | 1 paper | 2026 | Asked |
| 21 | Numericals: binding energy per nucleon and relative stabilityGiven the total binding energies of two nuclei, divide each by its mass number, compare the results and state that the nucleus with the larger binding energy per nucleon (not the larger total) is the more stable. | Numericals | 2 | 1 paper | 2025 improvement | Asked |
| 22 | Numericals: energy released in a nuclear reaction from massesFor a given fission or fusion reaction with the masses in u, check that A and Z balance, find the mass lost (mass of reactants minus mass of products) and convert it to the energy released in MeV using the value of 1 u; say whether the reaction is exothermic. | Numericals | 2 | 1 paper | 2024 | Asked |
| 23 | Nucleus definitions: composition, atomic mass, unified atomic mass unitState what a nucleus is made of (Z protons and A - Z neutrons, together called nucleons), define the unified atomic mass unit as one-twelfth of the mass of a carbon-12 atom with its value in kg, and say that atomic masses are expressed in u. | Statement | 1 | 1 paper | 2023 | Asked |
| 24 | Geiger-Marsden alpha-scattering experiment: set-up, observations, conclusionsDraw a labelled sketch of the set-up (alpha source in a lead block, narrow beam, thin gold foil, rotatable zinc sulphide screen with microscope), state the three observations (most alpha particles pass straight through, a few are deflected through large angles, about 1 in 8000 turns back through more than 90 deg) and write the conclusion drawn from each. | Device | 2 | 1 paper | 2019 | Asked |
| 25 | Rutherford's nuclear model: features and two drawbacksWrite the features of Rutherford's model (tiny, massive, positively charged nucleus; electrons revolve round it with the electrostatic attraction as centripetal force; atom neutral and mostly empty) and the two failures that led to Bohr's theory (a revolving electron is accelerated, so it should radiate and spiral into the nucleus; it should give a continuous spectrum, not the observed line spectrum of hydrogen). | Statement | 2 | 1 paper | 2019 | Asked |
| 26 | Derive kinetic, potential and total energy in nth orbitFrom the force equation obtain the kinetic energy, write the electrostatic potential energy, add them for the total energy, substitute r_n to express E_n in terms of n, and evaluate it as -13.6/n^2 eV. | Derivation | 3 | 1 paper | 2019 | Asked |
| 27 | Derive distance of closest approach of an alpha particleFor an alpha particle of kinetic energy (1/2) m v^2 heading straight at a nucleus of charge Ze, equate the kinetic energy lost to the electrostatic potential energy gained at the point where it stops, obtain r0, and state that r0 is an upper limit for the radius of the nucleus. | Derivation | 2 | never | Never asked | |
| 28 | Numericals: distance of closest approachGiven the kinetic energy of the alpha particle in MeV (or its speed) and Z of the target, convert the energy to joule and compute r0 in metre and in fermi; also do the reverse (energy for a given r0) and say how r0 changes when the energy or the target is changed. | Numericals | 2 | never | Never asked | |
| 29 | Atomic structure terms: Z, N, A and nuclide notationDefine atomic number Z, neutron number N, mass number A and nucleon, write the relation between them, write a nuclide in the form (A over Z) X, and read Z, N and A off a given symbol. | Statement | 1 | never | Never asked | |
| 30 | Obtain the Rydberg formula from Bohr's energy levelsUse h f = E_n2 - E_n1 with E_n = -m e^4/(8 epsilon0^2 n^2 h^2) to obtain 1/lambda = R (1/n1^2 - 1/n2^2), identify R in terms of m, e, epsilon0, h and c, and state that its value agrees with the experimental Rydberg constant. | Derivation | 2 | never | Never asked | |
| 31 | Numericals: Delta E, frequency and wavelength of a transitionFor an electron jumping between two given levels, compute Delta E in eV and in joule from E_n = -13.6/n^2 eV, then the frequency f = Delta E/h and the wavelength lambda = h c/Delta E in nm, and name the series and region the line belongs to. | Numericals | 2 | never | Never asked | |
| 32 | Numericals: nuclear radius and nuclear densityUsing R = R0 A^(1/3), compute the radius of a given nucleus, the ratio of the radii (and of the volumes) of two nuclei from their mass numbers, and the density of nuclear matter from the nucleon mass. | Numericals | 1 | never | Never asked | |
| 33 | Explain fission and fusion energy release from the BE curveUsing the shape of the BE per nucleon curve, explain in three or four lines why splitting a heavy nucleus into two middle-order nuclei, and fusing two light nuclei into a heavier one, both increase the binding energy per nucleon and therefore release energy (exothermic reactions). | Give reason | 2 | never | Never asked | |
| 34 | Calculate Q for fission from BE per nucleon valuesFor a heavy nucleus of A = 240 with BE/A about 7.6 MeV splitting into two equal fragments of A = 120 with BE/A about 8.5 MeV, compute the total binding energy before and after and hence the disintegration energy Q. | Numericals | 2 | never | Never asked | |
| 35 | Chain reaction: controlled versus uncontrolled, criticalitySay in two lines what a chain reaction is (neutrons released in one fission cause further fissions), what criticality means (on average exactly one neutron from each fission causes another, so the reaction just sustains itself), and compare a controlled chain reaction (nuclear reactor, steady release of energy) with an uncontrolled one (nuclear bomb, explosive release). | Comparison | 2 | never | Never asked | |
| 36 | Compare nuclear fission and nuclear fusion (table)Draw a table comparing fission and fusion on: what happens to the nuclei, which nuclei take part, the condition needed (slow neutron at ordinary temperature against very high temperature), energy released per reaction and per nucleon, whether it can be controlled, and one example of each (reactor and nuclear bomb against the Sun and hydrogen bomb). | Comparison | 2 | never | Never asked | |
| 37 | Bohr's quantisation condition from de Broglie wavesArgue that a stationary orbit must hold a whole number of de Broglie wavelengths of the electron (a standing wave round the orbit), write 2 pi r = n lambda with lambda = h/(m v), and obtain m v r = n h/(2 pi). | Derivation | 2 | 1 paper | 2025 improvement | Not in syllabus |
| 38 | Limitations of Bohr's theory (any two)State two limitations of Bohr's theory: it works only for hydrogen and hydrogen-like (one-electron) atoms; it does not explain the fine structure or the relative intensities of spectral lines; it does not explain the splitting of lines in magnetic and electric fields; it treats the electron only as a particle in a definite orbit. | Statement | 1 | 1 paper | 2026 | Not in syllabus |
This list was made from the 2027 syllabus and checked with 9 board papers, including the 2027 specimen paper. It is not yet checked with the textbook.
The 10 topics Physics papers ask most
Counted on the board papers from 2018 to the 2027 specimen paper, which every unit has been checked against.
- 1.Numericals: peak, rms, mean, frequency from an ac equationP4 Electromagnetic Induction and Alternating Currents · asked 7 times since 2018
- 2.Uses and special properties of each region (table)P5 Electromagnetic Waves · asked 7 times since 2018
- 3.State Bohr's postulates for the hydrogen atomP8 Atoms and Nuclei · asked 7 times since 2018
- 4.Magnetic force on a moving charge and Lorentz forceP3 Magnetic Effects of Current and Magnetism · asked 6 times since 2018
- 5.Numericals: average power and power factorP4 Electromagnetic Induction and Alternating Currents · asked 6 times since 2018
- 6.Doping, n-type and p-type, donors, acceptors, carriersP9 Electronic Devices · asked 6 times since 2018
- 7.Numericals: two-loop network with two batteries (Kirchhoff)P2 Current Electricity · asked 5 times since 2018
- 8.Derive B at the centre of a circular loopP3 Magnetic Effects of Current and Magnetism · asked 5 times since 2018
- 9.Numericals: B at the centre of a circular coilP3 Magnetic Effects of Current and Magnetism · asked 5 times since 2018
- 10.Ampere's law: derive B near a long straight wireP3 Magnetic Effects of Current and Magnetism · asked 5 times since 2018