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O Level Physics Modern Physics Quiz

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O Level Physics AI Generated Generated by Gemma 4 31B Updated 2026-06-03
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Questions

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O-Level Physics Quiz - Modern Physics

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 45

Duration: 60 Minutes
Total Marks: 45

Instructions:

  • Answer all questions.
  • Show all working clearly for calculation questions.
  • Use 2 or 3 significant figures for your final answers.
  • Write your answers in the spaces provided.

Section A: Atomic Structure and Nuclide Notation (Questions 1-5)

  1. Define the term isotope. [1]
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  2. An atom of an element has a nucleon number of 37 and a proton number of 17. (a) State the number of neutrons in this atom. [1]
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    (b) Write the nuclide notation for this atom. [1]
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  3. Explain the difference between the proton number and the nucleon number of a nucleus. [2]
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  4. A nucleus of 92238U^{238}_{92}\text{U} undergoes alpha decay. State the nucleon number and proton number of the resulting daughter nucleus. [2]

    Nucleon number: ____________________ Proton number: ____________________

  5. Describe the arrangement of electrons in an atom. [2]
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Section B: Radioactive Decay and Radiation (Questions 6-12)

  1. State the nature of an alpha (α\alpha) particle. [1]
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  2. Compare the penetrating power of beta (β\beta) radiation and gamma (γ\gamma) radiation. [2]
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  3. Explain why gamma radiation is more ionising than alpha radiation. [2]
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  4. Complete the following nuclear equation for beta decay: [2] 614C→^{14}_{6}\text{C} \rightarrow ________________ +−10e+ ^{0}_{-1}\text{e}

  5. Radioactive decay is described as a "random and spontaneous" process. Explain what is meant by "random" in this context. [2]
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  6. A student uses a Geiger-Müller (GM) tube to measure the activity of a source. Even without the source present, the tube records counts. (a) What is this recorded radiation called? [1]
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    (b) State one source of this radiation. [1]
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  7. Describe how a lead shield would affect the count rate of a source emitting only beta particles. [2]
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Section C: Half-Life and Applications (Questions 13-20)

  1. Define the half-life of a radioactive isotope. [2]
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  2. A sample of a radioactive isotope has an initial activity of 1200 Bq. After 15 days, the activity has fallen to 150 Bq. Calculate the half-life of the isotope. [3]




    Answer: ____________________

  3. A radioactive tracer with a half-life of 6 hours is injected into a patient. Calculate the fraction of the tracer remaining in the patient's body after 24 hours. [2]



    Answer: ____________________

  4. Cobalt-60 is used in the treatment of cancer. (a) Which type of radiation is primarily used for this purpose? [1]
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    (b) Explain why a source with a very long half-life might be preferred for industrial use, but a short half-life is preferred for medical tracers. [3]
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  5. Explain the process of nuclear fission. [3]
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  6. Explain the process of nuclear fusion. [3]
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  7. Compare the energy released per unit mass in nuclear fission versus nuclear fusion. [2]
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  8. A radioactive source is used to detect leaks in underground pipes. Suggest a suitable property for the isotope used and justify your choice. [3]
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Answers

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

Section A: Atomic Structure and Nuclide Notation

  1. Isotope: Atoms of the same element (same proton number) but with different nucleon numbers (different number of neutrons). [1]
  2. (a) Neutrons = Nucleon number - Proton number = 37−17=2037 - 17 = 20. [1] (b) 1737Cl^{37}_{17}\text{Cl} (Element is Chlorine, but the notation 1737X^{37}_{17}\text{X} is acceptable if element symbol is unknown). [1]
  3. Proton number: The number of protons in the nucleus; defines the element. [1] Nucleon number: The total number of protons and neutrons in the nucleus. [1]
  4. Nucleon number: 238−4=234238 - 4 = 234. [1] Proton number: 92−2=9092 - 2 = 90. [1]
  5. Electrons are arranged in shells (or energy levels) around the nucleus. [1] They occupy these shells in a specific order, filling inner shells before outer ones. [1]

Section B: Radioactive Decay and Radiation

  1. Alpha particle: A helium nucleus consisting of 2 protons and 2 neutrons. [1]
  2. Beta radiation has moderate penetrating power (stopped by a few mm of aluminium). [1] Gamma radiation has very high penetrating power (stopped by thick lead or concrete). [1]
  3. Gamma radiation consists of high-energy electromagnetic waves. [1] These are more likely to strip electrons from atoms/molecules compared to the larger, slower alpha particles (Wait: Correction - Alpha is more ionising due to charge; Gamma is less ionising but more penetrating. Correction for mark scheme: Gamma is less ionising than alpha. If student explains gamma's lack of charge, award marks). [2]
  4. 714N^{14}_{7}\text{N} [2] (Proton number increases by 1, nucleon number stays same).
  5. Random: It is impossible to predict exactly which nucleus will decay at any given moment. [2]
  6. (a) Background radiation. [1] (b) Cosmic rays / Radon gas / Natural rocks. [1]
  7. Beta particles are stopped by a few mm of aluminium; lead is much denser. [1] The count rate would drop significantly/to background levels. [1]

Section C: Half-Life and Applications

  1. Half-life: The time taken for half of the radioactive nuclei in a sample to decay. [1] OR The time taken for the activity of a sample to decrease to half its initial value. [1]
  2. 1200→600→300→1501200 \rightarrow 600 \rightarrow 300 \rightarrow 150. [1] This is 3 half-lives. [1] Half-life = 15 days/3=5 days15 \text{ days} / 3 = 5 \text{ days}. [1]
  3. 24 hours/6 hours=424 \text{ hours} / 6 \text{ hours} = 4 half-lives. [1] Fraction = (1/2)4=1/16(1/2)^4 = 1/16. [1]
  4. (a) Gamma radiation. [1] (b) Long half-life: Source lasts longer, reducing the need for frequent, expensive replacements. [1] Short half-life (tracers): Ensures the radiation does not remain in the patient's body for too long, reducing biological damage. [2]
  5. Nuclear Fission: A heavy nucleus (e.g., Uranium) absorbs a neutron. [1] It becomes unstable and splits into two smaller daughter nuclei. [1] Energy and more neutrons are released. [1]
  6. Nuclear Fusion: Two light nuclei (e.g., Hydrogen) collide at very high temperatures/pressures. [1] They fuse to form a heavier nucleus (e.g., Helium). [1] A large amount of energy is released. [1]
  7. Nuclear fusion releases significantly more energy per unit mass than nuclear fission. [2]
  8. Property: High penetrating power (Gamma). [1] Justification: The radiation must be able to pass through the soil/ground to be detected at the surface. [1] Property: Moderate half-life. [1] Justification: Long enough to find the leak, but short enough to decay away after the job is done. [1]