A Level Physics (A2) chapter 12: Nuclear physics MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
51 exam-style questions on 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.
Mass defect and nuclear binding energy26 questions
Radioactive decay25 questions
Ten 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. The mass defect of a carbon-12 nucleus (6 protons, 6 neutrons) is 0.0990 u. What is its binding energy per nucleon? (1 u = 1.66 × 10−27 kg)
A
7.70 MeV
B
15.4 MeV
C
92.4 MeV
D
1110 MeV
Show answer
Answer: A. Binding energy = 0.0990 × 1.66 × 10−27 × (3.00 × 108)2 = 1.48 × 10−11 J = 92.4 MeV; per nucleon 92.4 ÷ 12 = 7.70 MeV. Dividing by 6 (protons only) gives 15.4 MeV, and 92.4 MeV is the total.
2. A student measures the count from a radioactive source in several 10 s intervals and finds that the readings vary considerably. What is the best way to obtain a reliable value of the count rate?
A
take only the first reading, before the source has had time to decay
B
take the largest reading, since some decays will have been missed in the others
C
move the detector much closer to the source so that the readings stop varying
D
count for a much longer total time and divide the total count by the total time
Show answer
Answer: D. Decay is random, so the count in any interval fluctuates. Counting for a long time (a large total count) makes the fractional fluctuation small and gives a reliable mean rate. Moving closer increases the count but does not remove the randomness.
3. What is nuclear fission?
A
the joining together of two light nuclei to form a heavier nucleus, with the release of a large amount of energy
B
the emission of an α-particle by an unstable heavy nucleus, forming a lighter nucleus
C
the splitting of a heavy nucleus into two smaller nuclei, often after it absorbs a neutron
D
the emission of a gamma-ray photon as an excited nucleus falls to a lower energy state
Show answer
Answer: C. In fission a heavy nucleus such as uranium-235 splits into two medium-sized nuclei plus a few neutrons, releasing energy. Joining light nuclei is fusion.
4. In each fission in a nuclear reactor the total mass decreases by 0.20 u. The reactor produces a thermal power of 1.5 GW. How many fissions occur each second? (1 u = 1.66 × 10−27 kg)
A
8.3 × 10−8
B
8.0 × 106
C
5.0 × 1019
D
1.5 × 1028
Show answer
Answer: C. Energy per fission = 0.20 × 1.66 × 10−27 × (3.00 × 108)2 = 2.99 × 10−11 J, so the rate is 1.5 × 109 ÷ 2.99 × 10−11 = 5.0 × 1019 s−1. Using c instead of c2 gives 1.5 × 1028.
5. Which of these nuclei has the greatest binding energy per nucleon?
A
hydrogen-2
B
helium-4
C
uranium-238
D
iron-56
Show answer
Answer: D. The peak of the binding energy per nucleon curve is near nucleon number 56, so iron-56 is among the most stable nuclei. Helium-4 is high for a light nucleus but still well below iron; uranium-238 is lower than iron.
6. Why does nuclear fusion take place only at very high temperatures, such as those in the core of a star?
A
heat is needed to split the nuclei into separate nucleons before they can join together
B
the nuclei must move fast enough to overcome their electrostatic repulsion and get close enough to fuse
C
the high temperature supplies the binding energy that holds the product nucleus together
D
only at high temperatures do the nuclei have a mass defect that can be released as energy
Show answer
Answer: B. Nuclei are positively charged and repel each other. Only at very high temperatures do they have enough kinetic energy to come close enough for the short-range strong force to bind them.
7. A Geiger-Müller tube is placed near a long-lived radioactive source. The counts recorded in five successive 10 s intervals are 212, 198, 227, 205 and 190. What do the variations in these readings show?
A
radioactive decay is random
B
radioactive decay is spontaneous
C
the source has a very short half-life
D
the background count is increasing steadily
Show answer
Answer: A. The source is long-lived, so its activity is effectively constant, yet the counts fluctuate irregularly about a mean. This shows the random nature of decay. "Spontaneous" means that decay is not affected by external conditions, which these readings do not test.
8. In a fusion reaction, a hydrogen-2 nucleus (mass 2.01355 u) and a hydrogen-3 nucleus (mass 3.01550 u) form a helium-4 nucleus (mass 4.00151 u) and a neutron (mass 1.00867 u). How much energy is released? (1 u = 1.66 × 10−27 kg)
A
1.5 × 10−10 J
B
2.8 × 10−12 J
C
9.4 × 10−21 J
D
3.0 × 10−10 J
Show answer
Answer: B. Mass lost = (2.01355 + 3.01550) − (4.00151 + 1.00867) = 0.01887 u = 3.13 × 10−29 kg. E = Δmc2 = 2.8 × 10−12 J (about 17.6 MeV). Leaving out the neutron gives an enormous and wrong mass loss.
9. A uranium-235 nucleus absorbs a neutron and undergoes fission: 23592U + 10n → 14156Ba + 9236Kr + x 10n. What is x?
A
2
B
3
C
1
D
4
Show answer
Answer: B. Nucleon numbers must balance: 235 + 1 = 141 + 92 + x, so x = 3. Proton numbers already balance: 92 = 56 + 36. Forgetting the incoming neutron gives 2.
10. A student plots the corrected count rate from a source against time. A smooth exponential curve fits the general trend but the points lie scattered on both sides of it. What is the main reason for the scatter?
A
the half-life of the source changes slightly during the experiment
B
the count rate fluctuates because radioactive decay is random
C
the source decays faster when it is warmer
D
the detector counts every particle twice at high count rates
Show answer
Answer: B. Because each nucleus decays at random, the number of decays in a fixed interval fluctuates about the mean, so points scatter about the smooth curve. The half-life is a constant and is not affected by temperature.
51, each with the answer and a short explanation, across 2 topics: Mass defect and nuclear binding energy, Radioactive decay. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Physics (A2) chapter 12 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.
