NUST NET Physics chapter 8: Physics · Modern and nuclear physics MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

42 exam-style questions on Physics · Modern and nuclear 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.

42 questions · 3 topics · 10 per test

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What chapter 8 covers

Ten Physics · Modern and nuclear physics questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Energy is released both when a heavy nucleus splits (fission) and when light nuclei join (fusion), because in each case

  1. A
    the total number of nucleons decreases
  2. B
    the products have a greater binding energy per nucleon
  3. C
    the products have a smaller binding energy per nucleon
  4. D
    neutrons are turned completely into energy
Show answer

Answer: B. Binding energy per nucleon is greatest near iron-56. Splitting heavy nuclei or fusing light ones moves towards this peak, so the products are more tightly bound; the mass lost is released as energy. The number of nucleons does not change.

2. The Lyman series of hydrogen is produced by transitions that end on

  1. A
    n = 2, and lies in the visible
  2. B
    n = 1, and lies in the infrared
  3. C
    n = 1, and lies in the ultraviolet
  4. D
    n = 3, and lies in the infrared
Show answer

Answer: C. Lyman lines end on the ground state n = 1; these are the largest energy gaps, so the photons are in the ultraviolet. Transitions to n = 2 give the visible Balmer series.

3. The energy of the electron in the n-th orbit of hydrogen is En = −13.6/n2 eV. Its energy in the orbit n = 2 is

  1. A
    −6.8 eV
  2. B
    +3.4 eV
  3. C
    −3.4 eV
  4. D
    −1.51 eV
Show answer

Answer: C. E2 = −13.6/22 = −3.4 eV. −6.8 eV divides by n instead of n2, and −1.51 eV is the n = 3 level. Bound-state energies are negative.

4. In the fusion reaction 2H + 3H → 4He + X, the particle X is

  1. A
    a proton
  2. B
    an α-particle
  3. C
    an electron
  4. D
    a neutron
Show answer

Answer: D. Mass numbers: 2 + 3 = 4 + 1; charge numbers: 1 + 1 = 2 + 0. So X has A = 1 and Z = 0: a neutron. This deuterium–tritium fusion releases about 17.6 MeV.

5. In a Wilson cloud chamber, α-particles leave

  1. A
    thin, broken, twisted tracks
  2. B
    thick, straight tracks of nearly equal length
  3. C
    no visible tracks
  4. D
    long spiral tracks
Show answer

Answer: B. α-particles are heavy and ionise strongly, so they leave dense, straight tracks of about the same length (their range). β-particles give thin, twisted tracks, and γ-rays leave only short, scattered tracks from the electrons they knock out.

6. An X-ray tube works at 25 kV. Taking hc = 1240 eV nm, the shortest wavelength of the X-rays it produces is about

  1. A
    0.50 nm
  2. B
    50 nm
  3. C
    0.050 nm
  4. D
    0.0050 nm
Show answer

Answer: C. The shortest wavelength arises when an electron gives all its energy, 25 keV, to one photon: λmin = hc/eV = 1240/25 000 ≈ 0.050 nm. Forgetting the kilo in kV gives 50 nm.

7. A clock moves past an observer at 0.6c. Two ticks that are 8.0 s apart in the clock's own frame are measured by the observer to be

  1. A
    6.4 s apart
  2. B
    8.0 s apart
  3. C
    13.3 s apart
  4. D
    10 s apart
Show answer

Answer: D. t = t0/√(1 − v2/c2) = 8.0/√(1 − 0.36) = 8.0/0.8 = 10 s. Moving clocks run slow, so the observer measures a longer time; 6.4 s multiplies by 0.8 instead of dividing.

8. In the Bohr model of hydrogen, the speed of the electron in an orbit is inversely proportional to n. The ratio of its speed in the first orbit to that in the third orbit is

  1. A
    9
  2. B
    1/3
  3. C
    1/9
  4. D
    3
Show answer

Answer: D. v ∝ 1/n, so v1/v3 = 3/1 = 3. 9 comes from wrongly using the n2 dependence of the radius.

9. A rod 10 m long in its own frame moves along its length at 0.80c past an observer. The observer measures its length as

  1. A
    8.0 m
  2. B
    17 m
  3. C
    3.6 m
  4. D
    6.0 m
Show answer

Answer: D. L = L0√(1 − v2/c2) = 10 × √(1 − 0.64) = 10 × 0.6 = 6.0 m. Multiplying by v/c = 0.80 gives 8.0 m; dividing by 0.6 gives the dilated 17 m.

10. The activity of a radioactive sample falls from 1600 Bq to 100 Bq in 12 hours. Its half-life is

  1. A
    4.0 h
  2. B
    0.75 h
  3. C
    3.0 h
  4. D
    6.0 h
Show answer

Answer: C. 1600 → 800 → 400 → 200 → 100 is 4 half-lives in 12 h, so T½ = 3.0 h. Miscounting the halvings as 3 gives 4.0 h.

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Ways to practise this chapter

Physics · Modern and nuclear physics: questions students ask

How many Physics · Modern and nuclear physics MCQs are there?

42, each with the answer and a short explanation, across 3 topics: Dawn of modern physics, Atomic spectra, Nuclear physics. Every chapter test draws ten of them, so you can take it many times.

Is the NUST NET Physics chapter 8 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.

Can I read the explanations in Urdu?

Yes. In practice mode and on your results you can switch the explanations to Urdu.

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