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O Level Physics Modern Physics Quiz
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Questions
O-Level Physics Quiz - Modern Physics
Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 40
Duration: 45 minutes Total Marks: 40
Instructions:
- This quiz covers Topic 20: Radioactivity from the O-Level Physics (6091) syllabus.
- Answer ALL questions in the spaces provided.
- Show all working for calculation questions. Marks are awarded for method.
- Include units in all numerical answers.
- Use g = 10 m/s² where needed, unless otherwise stated.
- The number of marks for each question is shown in brackets.
Section A: Atomic Structure and Nuclear Physics (10 marks)
Answer all questions in this section.
1. State the relative charge and relative mass of a proton, a neutron, and an electron.
| Particle | Relative Charge | Relative Mass |
|---|---|---|
| Proton | ||
| Neutron | ||
| Electron |
[3 marks]
2. The nuclide notation for uranium-235 is shown below:
(a) State the proton number (atomic number) of this nuclide. [1 mark]
(b) State the nucleon number (mass number) of this nuclide. [1 mark]
(c) Calculate the number of neutrons in a uranium-235 nucleus. [1 mark]
3. Define the term isotopes. [2 marks]
4. Carbon-12 and carbon-14 are two isotopes of carbon. Explain why these two isotopes have the same chemical properties but different physical properties. [2 marks]
5. State the charge of an alpha particle and explain why it is strongly ionising. [2 marks]
Section B: Radioactive Decay and Nuclear Equations (10 marks)
Answer all questions in this section.
6. State what is meant by the term radioactive decay. [2 marks]
7. Complete the following nuclear equation for alpha decay of radium-226:
^{226}_{88}\text{Ra} \rightarrow \text{______} + \text{______}
[2 marks]
8. Complete the following nuclear equation for beta decay of carbon-14:
^{14}_{6}\text{C} \rightarrow \text{______} + \text{______} + \bar{\nu}_e
[2 marks]
9. A radioactive source emits beta particles.
(a) Describe the nature of a beta particle. [1 mark]
(b) State the penetrating power of beta radiation. [1 mark]
(c) Explain why beta radiation has a lower ionising effect than alpha radiation. [2 marks]
10. State what happens to the atomic number and mass number of a nucleus when it emits a gamma ray. [2 marks]
Section C: Properties of Radiation and Half-Life (10 marks)
Answer all questions in this section.
11. The table below compares alpha, beta, and gamma radiation. Complete the table by filling in the blanks labelled (i) to (iv).
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | Helium nucleus | (i) _______________ | Electromagnetic wave |
| Charge | +2 | (ii) _______________ | 0 |
| Penetrating power | Stopped by paper or a few cm of air | (iii) _______________ | Stopped by several cm of lead or thick concrete |
| Ionising effect | (iv) _______________ | Medium | Low |
[4 marks]
12. A radioactive sample has a half-life of 8 days. The initial mass of the sample is 64 g.
(a) Define the term half-life. [1 mark]
(b) Calculate the mass of the sample remaining after 24 days. [2 marks]
(c) Calculate the mass of the sample remaining after 40 days. [2 marks]
(d) Explain why the mass of the sample never reaches exactly zero, even after a very long time. [1 mark]
Section D: Applications, Hazards, and Nuclear Energy (10 marks)
Answer all questions in this section.
13. A doctor uses a radioactive tracer to investigate a patient's thyroid gland. The tracer emits gamma radiation and has a half-life of 6 hours.
(a) Explain why a gamma emitter is chosen rather than an alpha or beta emitter. [2 marks]
(b) Explain why a tracer with a half-life of 6 hours is suitable for this medical procedure. [2 marks]
14. Workers in a nuclear facility wear film badges. Explain the purpose of a film badge and how it works. [2 marks]
15. State two sources of background radiation. [2 marks]
16. Nuclear fission and nuclear fusion both release energy from the nucleus.
(a) Describe the process of nuclear fission. [1 mark]
(b) State one advantage of nuclear fusion over nuclear fission for power generation. [1 mark]
17. Explain why radioactive waste from nuclear power plants must be stored safely for many years. [2 marks]
18. Describe one way in which radiation is used to sterilise medical equipment. [2 marks]
19. State one safety precaution that should be taken when handling a radioactive source in a school laboratory. [1 mark]
20. Explain the difference between contamination and irradiation by a radioactive source. [2 marks]
END OF QUIZ
Check your answers carefully before submitting.
Answers
O-Level Physics Quiz - Modern Physics: Answer Key and Marking Scheme
Total Marks: 40
Section A: Atomic Structure and Nuclear Physics (10 marks)
1. State the relative charge and relative mass of a proton, a neutron, and an electron.
| Particle | Relative Charge | Relative Mass |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1840 (or negligible/≈0) |
Marking: 1 mark for each correct row (3 marks total). Accept "negligible" or "approximately 0" for electron relative mass.
2. The nuclide notation for uranium-235:
(a) Proton number (atomic number) = 92 ✓ [1 mark]
(b) Nucleon number (mass number) = 235 ✓ [1 mark]
(c) Number of neutrons = 235 - 92 = 143 ✓ [1 mark]
Marking: Award marks for correct numerical answers. No working required for parts (a) and (b). Part (c) requires subtraction shown or correct answer.
3. Define the term isotopes.
Answer: Isotopes are atoms of the same element that have the same number of protons (same proton number / atomic number) but different numbers of neutrons (different nucleon number / mass number). [2 marks]
Marking:
- 1 mark: same number of protons / same atomic number / same element
- 1 mark: different number of neutrons / different mass number
4. Carbon-12 and carbon-14 are isotopes. Explain why they have the same chemical properties but different physical properties.
Answer: Chemical properties are determined by the number of electrons (or electron configuration), which is the same for both isotopes since they have the same number of protons. Physical properties (such as mass and density) depend on the mass of the atom, which differs because carbon-14 has two more neutrons than carbon-12. [2 marks]
Marking:
- 1 mark: Chemical properties same because same number of electrons / same electron arrangement
- 1 mark: Physical properties different because different mass / different number of neutrons
5. State the charge of an alpha particle and explain why it is strongly ionising.
Answer: An alpha particle has a charge of +2. It is strongly ionising because it has a large mass and a +2 charge, which causes it to interact strongly with atoms as it passes through matter, easily removing electrons from atoms and creating many ion pairs per unit length. [2 marks]
Marking:
- 1 mark: charge of +2
- 1 mark: explanation linking large mass/charge to strong interaction and ionisation
Section B: Radioactive Decay and Nuclear Equations (10 marks)
6. State what is meant by the term radioactive decay.
Answer: Radioactive decay is the spontaneous and random process by which an unstable atomic nucleus emits radiation (alpha, beta, or gamma) to become more stable, often changing into a different element. [2 marks]
Marking:
- 1 mark: spontaneous and random process
- 1 mark: unstable nucleus emits radiation / changes to become more stable / may form a new element
7. Complete the nuclear equation for alpha decay of radium-226:
^{226}_{88}\text{Ra} \rightarrow \text{______} + \text{______}
Answer:
Marking: 1 mark for correct daughter nucleus (Rn-222 or element with mass 222 and atomic number 86), 1 mark for alpha particle (He-4 or α). [2 marks]
8. Complete the nuclear equation for beta decay of carbon-14:
^{14}_{6}\text{C} \rightarrow \text{______} + \text{______} + \bar{\nu}_e
Answer:
Marking: 1 mark for nitrogen-14 (mass 14, atomic number 7), 1 mark for beta particle (electron with mass 0, charge -1). Accept β⁻ for the beta particle. [2 marks]
9. A radioactive source emits beta particles.
(a) Nature of a beta particle: A beta particle is a fast-moving electron emitted from the nucleus. [1 mark]
(b) Penetrating power: Beta radiation has moderate penetrating power; it can be stopped by a few millimetres of aluminium. [1 mark]
(c) Why beta radiation has a lower ionising effect than alpha radiation: Beta particles have a much smaller mass and a charge of -1 (compared to alpha's +2). They interact less strongly with atoms as they travel through matter, producing fewer ion pairs per unit length. [2 marks]
Marking:
- 1 mark: smaller mass and/or smaller charge magnitude than alpha
- 1 mark: weaker interaction with atoms / produces fewer ion pairs per unit length
10. State what happens to the atomic number and mass number of a nucleus when it emits a gamma ray.
Answer: Both the atomic number and the mass number remain unchanged. Gamma emission involves only a release of energy from the nucleus, with no change in the number of protons or neutrons. [2 marks]
Marking: 1 mark for atomic number unchanged, 1 mark for mass number unchanged.
Section C: Properties of Radiation and Half-Life (10 marks)
11. Complete the table:
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | Helium nucleus | (i) Electron / fast-moving electron | Electromagnetic wave |
| Charge | +2 | (ii) -1 | 0 |
| Penetrating power | Stopped by paper or a few cm of air | (iii) Stopped by a few mm of aluminium | Stopped by several cm of lead or thick concrete |
| Ionising effect | (iv) High | Medium | Low |
Marking: 1 mark for each correct entry (4 marks total). Accept reasonable equivalent answers for (iii), e.g., "stopped by thin metal sheet".
12. Half-life = 8 days, initial mass = 64 g.
(a) Definition of half-life: The half-life of a radioactive substance is the time taken for half the nuclei in a sample to decay, or the time taken for the activity (or mass) of the sample to fall to half its initial value. [1 mark]
(b) Mass remaining after 24 days:
- Number of half-lives = 24 ÷ 8 = 3
- Mass remaining = 64 × (½)³ = 64 × ⅛ = 8 g [2 marks]
Marking: 1 mark for correct number of half-lives, 1 mark for correct final mass with unit.
(c) Mass remaining after 40 days:
- Number of half-lives = 40 ÷ 8 = 5
- Mass remaining = 64 × (½)⁵ = 64 × 1/32 = 2 g [2 marks]
Marking: 1 mark for correct number of half-lives, 1 mark for correct final mass with unit.
(d) Why mass never reaches exactly zero: Radioactive decay is a random process at the level of individual nuclei. The mass halves each half-life, approaching but never reaching zero mathematically (exponential decay). In practice, when only a few atoms remain, statistical fluctuations dominate, and the concept of half-life breaks down. [1 mark]
Marking: Accept "the mass keeps halving and never reaches zero" or "it approaches zero asymptotically" or "there will always be some undecayed nuclei remaining".
Section D: Applications, Hazards, and Nuclear Energy (10 marks)
13. Radioactive tracer for thyroid gland (gamma emitter, half-life 6 hours).
(a) Why gamma emitter is chosen:
- Alpha radiation cannot penetrate body tissue to be detected externally; it would be absorbed within the body.
- Beta radiation has limited penetrating power and would also be largely absorbed before reaching a detector outside the body.
- Gamma radiation is highly penetrating and can pass through body tissue to be detected by a gamma camera outside the body, allowing imaging of the thyroid gland. [2 marks]
Marking: 1 mark for explaining why alpha/beta are unsuitable (cannot penetrate/be detected externally), 1 mark for explaining why gamma is suitable (penetrates body tissue, can be detected externally).
(b) Why half-life of 6 hours is suitable:
- Long enough to allow the tracer to be prepared, administered, and to accumulate in the thyroid gland for imaging (procedure takes a few hours).
- Short enough that the radioactivity decays quickly after the procedure, minimising the patient's radiation dose and reducing long-term exposure risk. [2 marks]
Marking: 1 mark for "long enough for the procedure", 1 mark for "short enough to minimise radiation dose to patient".
14. Purpose of a film badge and how it works:
Answer: A film badge is used to monitor the cumulative radiation dose received by workers who are regularly exposed to radiation (e.g., in nuclear facilities or hospitals). It contains a piece of photographic film in a light-tight holder. When radiation strikes the film, it causes the film to darken (fog) upon development. The degree of darkening indicates the total radiation dose received over a period of time. [2 marks]
Marking: 1 mark for monitoring cumulative radiation dose, 1 mark for explanation involving photographic film darkening upon exposure to radiation.
15. State two sources of background radiation.
Answer: Any two from:
- Cosmic rays from space
- Radon gas from the ground
- Rocks and soil containing radioactive isotopes
- Food and water containing radioactive isotopes
- Medical procedures (e.g., X-rays)
- Nuclear weapons testing fallout
Marking: 1 mark for each correct source (2 marks total).
16. Nuclear fission and nuclear fusion.
(a) Describe the process of nuclear fission: Nuclear fission is the process in which a heavy, unstable nucleus (e.g., uranium-235) splits into two smaller nuclei after absorbing a neutron, releasing a large amount of energy and more neutrons. [1 mark]
(b) State one advantage of nuclear fusion over nuclear fission for power generation: Any one from:
- Fuel for fusion (e.g., isotopes of hydrogen) is more abundant than fission fuel (e.g., uranium).
- Fusion produces less long-lived radioactive waste than fission.
- Fusion does not involve a chain reaction, so there is no risk of a meltdown.
Marking: 1 mark for a valid advantage.
17. Explain why radioactive waste from nuclear power plants must be stored safely for many years.
Answer: Radioactive waste contains radioactive isotopes with long half-lives that continue to emit ionising radiation for thousands of years. This radiation is harmful to living organisms, causing cell damage, mutations, and cancer. Safe storage is necessary to isolate the waste from the environment and prevent contamination of air, water, and soil, protecting current and future generations. [2 marks]
Marking: 1 mark for long half-life/continues to emit radiation, 1 mark for harmful effects/protection of environment and health.
18. Describe one way in which radiation is used to sterilise medical equipment.
Answer: Medical equipment (e.g., syringes, bandages) is exposed to a high dose of gamma radiation from a source such as cobalt-60. The gamma rays kill bacteria, viruses, and other pathogens by damaging their DNA, thus sterilising the equipment without making it radioactive. The equipment can be sterilised while sealed in packaging. [2 marks]
Marking: 1 mark for exposure to gamma radiation, 1 mark for killing pathogens/sterilising without making equipment radioactive.
19. State one safety precaution that should be taken when handling a radioactive source in a school laboratory.
Answer: Any one from:
- Use tongs or forceps to handle the source to maximise distance from the body.
- Keep the source pointed away from yourself and others.
- Store the source in a lead-lined container when not in use.
- Wash hands thoroughly after handling.
- Do not eat or drink in the laboratory.
Marking: 1 mark for any valid safety precaution.
20. Explain the difference between contamination and irradiation by a radioactive source.
Answer: Contamination occurs when radioactive material physically gets onto or inside an object or living organism, making it radioactive. Irradiation occurs when an object or organism is exposed to radiation from an external source, but does not itself become radioactive. A contaminated object continues to emit radiation; an irradiated object does not. [2 marks]
Marking: 1 mark for correct definition of contamination (radioactive material present on/in object), 1 mark for correct definition of irradiation (exposure to radiation without becoming radioactive).