IB Diploma Physics chapter 5: Nuclear and quantum physics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
46 exam-style questions on Nuclear and quantum physics, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Nuclear and quantum physics questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Why is fusion only possible at extremely high temperatures and densities?
A
nuclei must move fast enough to overcome their electrostatic repulsion and collide often enough
B
neutrons are needed to slow the nuclei down
C
nuclei must move slowly so that they can bind together
D
strong magnetic fields are needed to attract the nuclei together
Show answer
Answer: A. Positive nuclei repel. Only at very high temperatures (about 107 K) are they fast enough to get within range of the strong force, and a high density makes collisions frequent.
2. Which describes the axes of a Hertzsprung–Russell (HR) diagram?
A
mass on the vertical axis against age on the horizontal axis
B
luminosity on the vertical axis against surface temperature on the horizontal axis, with temperature increasing to the left
C
luminosity against surface temperature, with temperature increasing to the right
D
luminosity on the vertical axis against distance from Earth on the horizontal axis
Show answer
Answer: B. The HR diagram plots luminosity (or absolute magnitude) against surface temperature, and by convention temperature decreases from left to right.
3. An electron in a hydrogen atom falls from the level at −3.4 eV to the level at −13.6 eV. What is the wavelength of the emitted photon? (h = 6.63 × 10−34 J s, c = 3.00 × 108 m s−1, e = 1.60 × 10−19 C)
A
73 nm
B
91 nm
C
365 nm
D
122 nm
Show answer
Answer: D. Photon energy = 13.6 − 3.4 = 10.2 eV = 1.63 × 10−18 J. λ = hc/E = 1.99 × 10−25 ÷ 1.63 × 10−18 = 1.22 × 10−7 m = 122 nm. 73 nm adds the energies instead of subtracting.
4. Why does a main-sequence star stay the same size for millions of years?
A
magnetic forces hold it at a fixed size
B
it spins fast enough for outward forces to balance gravity
C
no forces act on the material of the star
D
the inward pull of gravity is balanced by the outward pressure of radiation and hot gas produced by fusion
Show answer
Answer: D. A stable star is in hydrostatic equilibrium: gravity tries to collapse it while radiation and gas pressure from fusion in the core push outwards.
5. The activity of a sample falls from 800 Bq to 50 Bq in 12 hours. What is its half-life?
A
6.0 h
B
3.0 h
C
4.0 h
D
1.5 h
Show answer
Answer: B. 800 → 400 → 200 → 100 → 50 is four half-lives in 12 h, so the half-life = 12 ÷ 4 = 3.0 h. 4.0 h wrongly counts three halvings.
6. What is the expected final stage of a star like the Sun?
A
a main-sequence star forever, since it has plenty of hydrogen
B
a red supergiant, then a supernova leaving a neutron star
C
a red giant, then a planetary nebula leaving a white dwarf
D
a supernova leaving a black hole
Show answer
Answer: C. Low-mass stars swell into red giants, shed their outer layers as a planetary nebula, and leave a hot, dense white dwarf. Supernovae happen only to much more massive stars.
7. Why was a very thin gold foil used in the Geiger–Marsden experiment?
A
so that each alpha particle was likely to be scattered by no more than one nucleus
B
because a thicker foil would reflect every alpha particle back
C
so that the alpha particles gained energy as they passed through
D
so that the foil would not become electrically charged
Show answer
Answer: A. A thin foil, only a few hundred atoms thick, means most particles interact with at most one nucleus, so the scattering angles can be interpreted simply.
8. Why can the stellar parallax method be used only for relatively nearby stars?
A
light from distant stars is too redshifted
B
for distant stars the parallax angle is too small to measure accurately
C
distant stars are hidden behind nearer ones
D
distant stars do not move across the sky
Show answer
Answer: B. Parallax angle p = 1/d, so it shrinks as distance grows. Beyond a few hundred parsecs the angles are too small for ground-based telescopes to measure.
9. Which statement about the strong nuclear force is correct?
A
it acts only between protons
B
it is attractive between nucleons and acts only over very short distances, about 10−15 m
C
it has a long range, like gravity
D
it is repulsive between neutrons
Show answer
Answer: B. The strong force binds protons and neutrons alike, overcoming proton–proton repulsion within a nucleus, but it falls to almost nothing beyond a few femtometres.
10. The mass defect of a helium-4 nucleus is 0.0304 u. What is its binding energy per nucleon? (1 u = 931.5 MeV c−2)
A
7.1 MeV
B
14 MeV
C
0.0076 MeV
D
28 MeV
Show answer
Answer: A. Binding energy = 0.0304 × 931.5 = 28.3 MeV. Helium-4 has 4 nucleons: 28.3 ÷ 4 = 7.1 MeV per nucleon. 28 MeV is the total; 14 MeV divides by the 2 protons only.
Nuclear and quantum physics: questions students ask
How many Nuclear and quantum physics MCQs are there?
46, each with the answer and a short explanation, across 4 topics: E.1 Structure of the atom, E.3 Radioactive decay, E.4 Fission, E.5 Fusion and stars. Every chapter test draws ten of them, so you can take it many times.
Is the IB Diploma Physics chapter 5 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
