O Level Physics Modern Physics Quiz

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O-Level Physics Quiz - Modern Physics

Name: ___________________________
Class: ___________________________
Date: ___________________________
Score: ___________ / 40

Duration: 50 minutes
Total Marks: 40

Instructions:

• Answer all 20 questions.
• Section A: Multiple-choice (1 mark each).
• Section B: Structured questions (2 marks each).
• Section C: Extended response (3–4 marks each).
• Show all working where calculation is required.
• Use SI units and proper notation.

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Section A: Multiple Choice (Questions 1–5)

1. Which of the following is a type of nuclear radiation that has no mass and no charge? [1]
   A. Alpha particle
   B. Beta particle
   C. Gamma ray
   D. Proton

   Answer: ______

2. The half-life of a radioactive isotope is the time taken for [1]
   A. all the nuclei to decay.
   B. half the nuclei present to decay.
   C. the mass to double.
   D. the radiation to stop.

   Answer: ______

3. In a smoke detector, the radioactive source commonly used is [1]
   A. uranium-238.
   B. americium-241.
   C. carbon-14.
   D. cobalt-60.

   Answer: ______

4. Which radiation is most easily stopped by a sheet of paper? [1]
   A. Gamma ray
   B. Beta particle
   C. Alpha particle
   D. Neutron

   Answer: ______

5. A nucleus emits a beta particle. The atomic number of the nucleus [1]
   A. decreases by 1.
   B. increases by 1.
   C. stays the same.
   D. decreases by 2.

   Answer: ______

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Section B: Structured Questions (Questions 6–15)

6. State one use of gamma rays in medicine. [2]

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7. A radioactive sample has a half-life of 4 hours. Calculate the fraction of the sample remaining after 12 hours. [2]
   Working: ______________________________________________________
   Answer: ______

8. Complete the nuclear equation for alpha decay of radon-222:
   $^{222}_{86}\text{Rn} \rightarrow ^{A}_{Z}\text{Po} + ^{4}_{2}\alpha$ [2]
   A = ______ Z = ______

9. Explain why alpha radiation is unsuitable for medical imaging inside the body but suitable for smoke detectors. [2]

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10. A Geiger-Müller tube is used to detect radiation. State what type of radiation it can detect. [2]

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11. The count rate from a source is 800 counts/s. After 2 half-lives, what is the count rate? [2]
    Working: ______________________________________________________
    Answer: ______ counts/s

12. State the penetration power of beta particles in order from least to most stopping material. [2]

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13. A sample contains $4.0 \times 10^{12}$ radioactive nuclei. After one half-life, how many remain? [2]
    Working: ______________________________________________________
    Answer: ______

14. Give one safety precaution when handling radioactive sources in school labs. [2]

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15. Identify the radiation that is deflected towards a negatively charged plate in an electric field. [2]
    Answer: ______

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Section C: Extended Response (Questions 16–20)

16. A hospital uses cobalt-60 to sterilise medical equipment.
    (a) State the type of radiation emitted. [1]
    (b) Explain why this radiation is effective for sterilisation. [2]
    (c) State one safety measure for workers. [1]

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17. The graph shows the decay of a radioactive isotope.

Image pending generation: graph for 17.

(a) Determine the half-life from the graph. [1]
(b) Calculate the count rate at 8 hours. [2]
(c) Explain why the curve never reaches zero. [1]

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18. Compare alpha, beta, and gamma radiation in terms of:
    (a) nature,
    (b) penetration,
    (c) ionising power. [3]

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19. A rock contains uranium-238 which decays to lead-206. Explain how this is used to estimate the age of the rock. [3]

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20. A student suggests using beta radiation to check the thickness of paper in a factory.
    (a) Explain how this works. [2]
    (b) State why gamma would be less suitable than beta for thin paper. [2]

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O-Level Physics Quiz - Modern Physics: Answer Key

Total Marks: 40
Topic: Modern Physics (Radioactivity)

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Section A: Multiple Choice

1. C [1]
   Gamma ray is electromagnetic radiation with no mass and no charge. Alpha is helium nucleus ($^4_2\alpha$), beta is electron ($^0_{-1}\beta$), proton has charge.

2. B [1]
   Half-life = time for half the radioactive nuclei present to decay. Not all decay at once.

3. B [1]
   Americium-241 emits alpha used in ionization chamber of smoke detectors.

4. C [1]
   Alpha stopped by paper; beta needs aluminium; gamma needs lead.

5. B [1]
   Beta decay: neutron → proton + electron, so atomic number Z increases by 1.

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Section B: Structured

6. [2]
   Use: killing cancer cells / tumour treatment (radiotherapy).
   Mark: 1 for context, 1 for correct medical use.

7. [2]
   Working: 12 h ÷ 4 h = 3 half-lives. Fraction = $(1/2)^3 = 1/8$.
   Answer: 1/8.
   Mark: 1 for number of half-lives, 1 for fraction.

8. [2]
   A = 222 – 4 = 218; Z = 86 – 2 = 84.
   Mark: 1 each.

9. [2]
   Alpha absorbed by few cm air / paper, cannot exit body for imaging; in smoke detector, alpha ionises air in small chamber to detect smoke.
   Mark: 1 each point.

10. [2]
    Detects alpha, beta, gamma (all ionising radiation).
    Mark: 2 for all three, 1 for partial.

11. [2]
    Working: after 1 half-life: 400; after 2: 200.
    Answer: 200 counts/s.
    Mark: 1 working, 1 answer.

12. [2]
    Paper (alpha) → aluminium (beta) → thick lead (gamma).
    Mark: 2 for correct order, 1 partial.

13. [2]
    Working: $4.0 \times 10^{12} \div 2 = 2.0 \times 10^{12}$.
    Answer: $2.0 \times 10^{12}$.
    Mark: 1 working, 1 answer.

14. [2]
    Use tongs / store in lead box / limit exposure time.
    Mark: 2 for specific, 1 vague.

15. [2]
    Alpha (positive) deflected to negative plate; beta negative to positive. Answer: alpha.
    Mark: 2 correct, 1 wrong sign.

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Section C: Extended

16. [4 total: 1+2+1]
    (a) Gamma rays. [1]
    (b) High penetration kills microbes on equipment without contact. [2]
    (c) Lead shielding / remote handling. [1]

17. [4 total: 1+2+1]
    (a) Half-life = 2 h (from 1000→500). [1]
    (b) At 8 h = 4 half-lives: 1000→500→250→125→62.5. [2]
    (c) Random decay; some nuclei always remain. [1]

18. [3]
    (a) Alpha: helium nucleus; Beta: electron; Gamma: EM wave. [1]
    (b) Alpha: paper; Beta: aluminium; Gamma: lead. [1]
    (c) Alpha strongest ionising, gamma weakest. [1]

19. [3]
    Measure ratio U-238/Pb-206; assume no initial lead; use half-life to calculate elapsed time. [3 points]

20. [4 total: 2+2]
    (a) Beta passes through paper; thickness change alters count detected, feedback controls roller. [2]
    (b) Gamma too penetrating, less change in count for thin paper, poor sensitivity. [2]