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Secondary 3 Physics Modern Physics Quiz
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Questions
Secondary 3 Physics Quiz - Modern Physics
Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 40
Duration: 45 minutes Total Marks: 40
Instructions:
- Answer ALL questions in the spaces provided.
- Show all working for calculation questions.
- Take g = 10 m/s² where required.
- The number of marks is given in brackets [ ] at the end of each question or part question.
Section A: Atomic Structure and Radioactivity (10 marks)
1. The diagram below shows a simplified model of an atom.
[Diagram: Central nucleus labeled with protons and neutrons, surrounding shells with electrons]
(a) Name the three subatomic particles labeled in the diagram. [1]
(b) State the relative charge and relative mass of each particle. [3]
| Particle | Relative Charge | Relative Mass |
|---|---|---|
| Proton | ||
| Neutron | ||
| Electron |
(c) The atom shown has 6 protons and 6 neutrons. State its nucleon number and proton number. [2]
Nucleon number: _________ Proton number: _________
2. A radioactive source emits three types of radiation: alpha (α), beta (β), and gamma (γ).
(a) State which type of radiation has the greatest ionising power. [1]
(b) State which type of radiation can be stopped by a few millimetres of aluminium but not by paper. [1]
(c) Explain why gamma radiation is the most penetrating of the three types. [2]
3. Complete the table below comparing alpha, beta, and gamma radiation. [2]
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | Helium nucleus | Electromagnetic wave | |
| Charge | -1 |
4. An atom of uranium-238 (²³⁸₉₂U) decays by emitting an alpha particle.
(a) Write the nuclear equation for this decay. [2]
(b) State the proton number and nucleon number of the daughter nucleus. [1]
Proton number: _________ Nucleon number: _________
5. Explain why some nuclei are unstable and undergo radioactive decay. [2]
Section B: Radioactive Decay and Half-Life (10 marks)
6. A radioactive isotope of iodine, I-131, has a half-life of 8 days. A sample initially contains 800 mg of I-131.
(a) Define the term half-life. [2]
(b) Calculate the mass of I-131 remaining after 24 days. [3]
Working:
Mass remaining: _________ mg
(c) Explain why the mass of the sample does not decrease to zero, even after many half-lives. [2]
7. The graph below shows the decay curve for a radioactive sample.
[Graph: Activity (counts per minute) on y-axis, Time (days) on x-axis.
Curve starts at 800 cpm at t=0, drops to 400 cpm at t=5 days,
200 cpm at t=10 days, 100 cpm at t=15 days]
(a) Use the graph to determine the half-life of the sample. [1]
Half-life: _________ days
(b) Calculate the activity of the sample after 20 days. [2]
Working:
Activity: _________ cpm
8. State one safety precaution that should be taken when handling radioactive materials and explain why it is necessary. [2]
9. A radioactive source has an initial activity of 1600 Bq. After 30 minutes, its activity is 200 Bq. Calculate the half-life of the source in minutes. [2]
Working:
Half-life: _________ minutes
10. Explain the difference between radioactive contamination and irradiation. [2]
Section C: Nuclear Reactions and Applications (10 marks)
11. The equation below represents a nuclear fission reaction:
²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3¹₀n + energy
(a) State what is meant by nuclear fission. [2]
(b) Explain why this reaction is described as a chain reaction. [2]
(c) State one advantage and one disadvantage of using nuclear fission to generate electricity. [2]
Advantage: _________________________________________________________
Disadvantage: _________________________________________________________
12. Nuclear fusion occurs in the core of stars, including the Sun.
(a) State what is meant by nuclear fusion. [2]
(b) Explain why extremely high temperatures are required for nuclear fusion to occur. [2]
13. State one similarity and one difference between nuclear fission and nuclear fusion. [2]
Similarity: _________________________________________________________
Difference: _________________________________________________________
14. Carbon-14 dating is used to determine the age of ancient organic materials.
(a) State the half-life of carbon-14. [1]
(b) Explain why carbon-14 dating cannot be used to date rocks that are millions of years old. [2]
15. Describe how a nuclear reactor controls the rate of the fission chain reaction. [2]
Section D: Uses and Hazards of Radioactivity (10 marks)
16. Radioactive sources are used in medicine for both diagnosis and treatment.
(a) State one medical use of a radioactive isotope and explain why its half-life is suitable for this purpose. [3]
(b) A patient is injected with a radioactive tracer that emits gamma radiation. Explain why an alpha emitter would NOT be suitable for this purpose. [2]
17. The table below shows the radiation dose received from various sources.
| Source | Dose (mSv per year) |
|---|---|
| Natural background radiation | 2.4 |
| Chest X-ray | 0.1 |
| CT scan | 10.0 |
| Airline crew (annual) | 3.0 |
(a) Calculate how many chest X-rays would give the same radiation dose as one CT scan. [1]
Number of chest X-rays: _________
(b) Explain why airline crew receive a higher annual radiation dose than most people on the ground. [2]
18. State two ways in which radioactive waste from nuclear power plants is managed to protect the environment. [2]
19. Explain why a radioactive source used in a smoke detector should have a long half-life. [2]
20. A student suggests that all uses of radioactive materials should be banned because of the associated risks. Discuss whether you agree with this statement, giving reasons for your answer. [2]
END OF QUIZ
Answers
Secondary 3 Physics Quiz - Modern Physics: ANSWER KEY
Total Marks: 40
Section A: Atomic Structure and Radioactivity (10 marks)
1. (a) Proton, neutron, electron [1 mark - all three required]
(b) [3 marks - 1 mark per correct row]
| Particle | Relative Charge | Relative Mass |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1840 (or negligible / ~0) |
(c) Nucleon number: 12 [1 mark] Proton number: 6 [1 mark]
2. (a) Alpha (α) radiation [1 mark]
(b) Beta (β) radiation [1 mark]
(c) Gamma radiation is an electromagnetic wave with no mass and no charge [1 mark]. It interacts weakly with matter, so it can pass through most materials without being absorbed, making it highly penetrating [1 mark].
3. [2 marks - 1 mark per correct row]
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | Helium nucleus | Electron (or fast-moving electron) | Electromagnetic wave |
| Charge | +2 | -1 | 0 |
4. (a) ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He [2 marks - 1 mark for correct daughter nucleus, 1 mark for correct alpha particle and balanced equation]
(b) Proton number: 90 [0.5 mark] Nucleon number: 234 [0.5 mark]
5. Nuclei are unstable when they have an imbalance of protons and neutrons [1 mark]. The nucleus has too much energy and undergoes radioactive decay to become more stable by emitting radiation [1 mark].
Section B: Radioactive Decay and Half-Life (10 marks)
6. (a) Half-life is the time taken for half the nuclei in a radioactive sample to decay [1 mark], or the time taken for the activity of a radioactive sample to fall to half its initial value [1 mark].
(b) Number of half-lives = 24 ÷ 8 = 3 half-lives [1 mark] After 1 half-life: 800 ÷ 2 = 400 mg After 2 half-lives: 400 ÷ 2 = 200 mg After 3 half-lives: 200 ÷ 2 = 100 mg [1 mark for correct method] Mass remaining: 100 mg [1 mark for correct answer]
(c) Radioactive decay is a random process [1 mark]. As the number of undecayed nuclei decreases, the activity decreases, but there is always a finite probability that some nuclei remain undecayed. The mass approaches zero asymptotically but never reaches exactly zero in a finite time [1 mark].
7. (a) Half-life: 5 days [1 mark - accept value read from graph where activity halves]
(b) After 20 days: 20 ÷ 5 = 4 half-lives [1 mark] Activity = 800 × (½)⁴ = 800 × 1/16 = 50 cpm [1 mark]
8. Use tongs/forceps to handle sources / keep source at arm's length / store in lead-lined container [1 mark]. This minimises exposure time and increases distance from the source, reducing the radiation dose received by the handler [1 mark]. [Accept any valid precaution with correct explanation]
9. Initial activity = 1600 Bq, final activity = 200 Bq 1600 → 800 → 400 → 200 (3 half-lives) [1 mark] Time = 30 minutes, so half-life = 30 ÷ 3 = 10 minutes [1 mark]
10. Contamination occurs when radioactive material gets onto or into an object or person [1 mark]. Irradiation occurs when a person or object is exposed to radiation from a source, but does not become radioactive itself [1 mark].
Section C: Nuclear Reactions and Applications (10 marks)
11. (a) Nuclear fission is the splitting of a large, unstable nucleus [1 mark] into two (or more) smaller nuclei, releasing energy and neutrons in the process [1 mark].
(b) The reaction produces neutrons (3 neutrons in this case) [1 mark]. These neutrons can go on to cause further fission reactions in other U-235 nuclei, which in turn produce more neutrons, creating a self-sustaining chain reaction [1 mark].
(c) Advantage: Produces large amounts of energy from small amounts of fuel / does not produce greenhouse gases during operation / reliable baseload power [1 mark for any valid advantage]. Disadvantage: Produces radioactive waste that must be stored safely for thousands of years / risk of catastrophic accidents (e.g., meltdown) / high decommissioning costs [1 mark for any valid disadvantage].
12. (a) Nuclear fusion is the process in which two light nuclei [1 mark] combine to form a heavier nucleus, releasing energy in the process [1 mark].
(b) Nuclei are positively charged and repel each other due to electrostatic repulsion [1 mark]. Extremely high temperatures give the nuclei sufficient kinetic energy to overcome this repulsion and come close enough for the strong nuclear force to bind them together [1 mark].
13. Similarity: Both release energy / both involve changes in the nucleus [1 mark]. Difference: Fission splits a large nucleus, while fusion combines small nuclei / fission produces radioactive waste, fusion produces less radioactive waste [1 mark for any valid difference].
14. (a) Half-life of carbon-14: 5730 years [1 mark]
(b) After millions of years, the amount of carbon-14 remaining in a sample would be too small to measure accurately [1 mark]. The half-life of carbon-14 is relatively short compared to millions of years, so nearly all the carbon-14 would have decayed [1 mark].
15. Control rods (made of boron or cadmium) are inserted into the reactor core to absorb neutrons [1 mark]. By adjusting the depth of the control rods, the number of neutrons available to cause further fission reactions is controlled, thus controlling the rate of the chain reaction [1 mark].
Section D: Uses and Hazards of Radioactivity (10 marks)
16. (a) Any valid medical use, e.g.: - Iodine-131 for treating thyroid cancer / investigating thyroid function [1 mark] - Technetium-99m for medical imaging/tracing [1 mark] - Explanation of half-life suitability: The half-life is short enough that the patient is not exposed to radiation for an unnecessarily long time, but long enough for the diagnostic procedure or treatment to be completed [1 mark]. [Accept other valid examples with correct half-life reasoning]
(b) Alpha radiation has very low penetrating power and cannot pass through skin [1 mark]. An alpha emitter injected into the body would not be detectable outside the body, making it useless as a tracer for external detection [1 mark].
17. (a) Number of chest X-rays = 10.0 ÷ 0.1 = 100 [1 mark]
(b) At high altitudes, the atmosphere is thinner and provides less shielding from cosmic radiation from space [1 mark]. Airline crew spend many hours at high altitudes, so they receive a higher cumulative dose of cosmic radiation compared to people at ground level [1 mark].
18. Any two valid methods:
- Stored in sealed containers and buried deep underground in geologically stable areas [1 mark].
- Vitrification (mixing waste with glass-forming materials to create a stable solid) before storage [1 mark]. [Accept other valid methods such as cooling in storage ponds, reprocessing, etc.]
19. A smoke detector needs to function reliably for many years without replacement [1 mark]. A source with a long half-life will maintain a relatively constant activity over the detector's lifetime, ensuring consistent performance [1 mark].
20. Disagree. While radioactive materials pose risks such as radiation sickness and cancer, their benefits in medicine (diagnosis and treatment), industry (non-destructive testing, smoke detectors), and energy generation are significant [1 mark]. With proper safety precautions, regulations, and waste management, the risks can be minimised, making the benefits outweigh the risks [1 mark]. [Accept any well-reasoned argument]
END OF ANSWER KEY