O Level Physics Modern Physics Quiz

<!-- TuitionGoWhere generation metadata: stage=3-0; model=google/gemma-4-31b-it; model_label=Gemma 4 31B; generated=2026-05-30; Sources: Stage 2-1 real exam-derived templates and Stage 2-2 exam-enriched syllabus. -->

O-Level Physics Quiz - Modern Physics

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 40

Duration: 60 Minutes
Total Marks: 40 Marks

Instructions:

• Answer all questions.
• For calculation questions, show all working clearly.
• Use 2 or 3 significant figures for your final answers.
• State the units for all numerical answers.

---

Section A: Multiple Choice & Short Answer (Questions 1-10)

Focus: Atomic Structure and Radiation Properties

1. Which of the following particles is composed of two protons and two neutrons? (a) Beta particle (b) Gamma ray (c) Alpha particle (d) Electron [1] Answer: ________

2. Define the term isotope. [1] Answer: ___________________________________________________________________________

3. State the nucleon number and proton number of an atom of Carbon-14. [1] Nucleon Number: ________ Proton Number: ________

4. Which type of radiation has the highest ionizing power? [1] Answer: ___________________________________________________________________________

5. Arrange alpha ($\alpha$), beta ($\beta$), and gamma ($\gamma$) radiation in order of increasing penetrating power. [1] Answer: ___________________________________________________________________________

6. A radioactive nucleus emits a beta particle. Describe the change in the proton number and nucleon number of the nucleus. [2] Answer: ___________________________________________________________________________

7. What is the nature of gamma radiation? [1] Answer: ___________________________________________________________________________

8. Explain why background radiation is present in a laboratory even when no radioactive sources are nearby. [2] Answer: ___________________________________________________________________________

9. Which particle is most likely to be stopped by a thin sheet of aluminum? [1] Answer: ___________________________________________________________________________

10. State one property of radioactive decay that makes it impossible to predict when a specific nucleus will decay. [1] Answer: ___________________________________________________________________________

---

Section B: Structured Response (Questions 11-15)

Focus: Half-life and Decay Equations

11. A sample of Iodine-131 has a half-life of 8 days. If the initial activity is $1.6 \times 10^5$ Bq, calculate the activity after 24 days. [2] Working:

    Answer: ____________________

12. Complete the following nuclear equation for the decay of Americium-241: $^{241}_{95}\text{Am} \rightarrow \text{X} + ^{4}_{2}\text{He}$ Identify the symbol and nucleon number of the daughter nucleus X. [2] Answer: ____________________

13. A radioactive isotope has a half-life of 15 minutes. After 45 minutes, only 12.5% of the original mass remains. Explain this result in terms of half-lives. [2] Answer: ___________________________________________________________________________

14. Compare the effect of alpha radiation and gamma radiation on human tissue. [2] Answer: ___________________________________________________________________________

15. A student uses a Geiger-Müller tube to measure a source. The background count is 20 counts/min and the total count is 120 counts/min. Calculate the corrected count rate. [2] Working:

    Answer: ____________________

---

Section C: Application and Analysis (Questions 16-20)

Focus: Nuclear Fusion, Fission, and Safety

16. Distinguish between nuclear fission and nuclear fusion. [2] Answer: ___________________________________________________________________________

17. In a nuclear reactor, what is the purpose of the control rods? [2] Answer: ___________________________________________________________________________

18. A radioactive isotope with a very short half-life (seconds) is used in medical imaging. Explain why a short half-life is preferred for this application. [2] Answer: ___________________________________________________________________________

19. Explain why a person working in a nuclear power plant wears a film badge (dosimeter). [2] Answer: ___________________________________________________________________________

20. Describe how the energy is released during a nuclear fission process. [2] Answer: ___________________________________________________________________________

<!-- TuitionGoWhere generation metadata: stage=3-0; model=google/gemma-4-31b-it; model_label=Gemma 4 31B; generated=2026-05-30; Sources: Stage 2-1 real exam-derived templates and Stage 2-2 exam-enriched syllabus. -->

O-Level Physics Quiz - Modern Physics (Answer Key)

1. (c) Alpha particle [1]

2. Atoms of the same element (same proton number) with different nucleon numbers (different number of neutrons). [1]

3. Nucleon Number: 14; Proton Number: 6 [1]

4. Alpha radiation [1]

5. Alpha $\rightarrow$ Beta $\rightarrow$ Gamma [1]

6. Proton number increases by 1; Nucleon number remains unchanged. [2]

7. High-energy electromagnetic waves / photons. [1]

8. Presence of cosmic rays from space and naturally occurring radioactive isotopes in the environment (e.g., rocks, soil). [2]

9. Beta particles [1]

10. Radioactive decay is random and spontaneous. [1]

11. 24 days / 8 days = 3 half-lives. $1.6 \times 10^5 \rightarrow 0.8 \times 10^5 \rightarrow 0.4 \times 10^5 \rightarrow 0.2 \times 10^5$ Bq. Answer: $2.0 \times 10^4$ Bq [2]

12. $^{237}_{93}\text{Np}$ (Neptunium). Nucleon number: 237. [2]

13. 45 mins / 15 mins = 3 half-lives. After 1st: 50%, 2nd: 25%, 3rd: 12.5%. [2]

14. Alpha radiation is highly ionizing and causes significant damage to cells but has low penetration (stopped by skin). Gamma radiation is weakly ionizing but highly penetrating, potentially damaging internal organs. [2]

15. Corrected count = Total count - Background count = $120 - 20 = 100$ counts/min. [2]

16. Fission: A heavy nucleus splits into two lighter nuclei. Fusion: Two light nuclei combine to form a heavier nucleus. [2]

17. To absorb neutrons and regulate the rate of the chain reaction to prevent the reactor from overheating. [2]

18. To ensure the radiation does not remain in the patient's body for too long, reducing the total dose of radiation exposure. [2]

19. To monitor the cumulative amount of ionizing radiation the worker has been exposed to over time to ensure it stays within safety limits. [2]

20. The mass of the products is slightly less than the mass of the original nucleus; this "mass defect" is converted into energy according to $E=mc^2$. [2]