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:

• This quiz contains 20 questions on Modern Physics (Radioactivity and the nuclear model).
• Section A: Multiple-choice (1–5). Section B: Structured short answers (6–15). Section C: Extended responses (16–20).
• Show all working where calculation is required.
• Use the blank spaces provided to write your answers.

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Section A: Multiple-Choice (1 mark each)

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

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

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3. Which radiation is most strongly deflected by a magnetic field?
A. Alpha
B. Beta
C. Gamma
D. All equally

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4. A nucleus of uranium-238 can be represented as $_{92}^{238}\text{U}$. How many neutrons does it have?
A. 92
B. 146
C. 238
D. 330

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5. Which of the following is a safe use of radioactivity in daily life?
A. Painting watch hands with radium
B. Using gamma rays to sterilise medical equipment
C. Putting radioactive sources in food for flavour
D. Using alpha sources to power home heaters

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Section B: Structured Short Answers (2 marks each)

6. State one property of alpha particles and one property of gamma rays.
Alpha: ________________________________________
Gamma: ________________________________________

7. A radioactive source has a half-life of 4 days. If the initial count rate is 800 counts/s, what is the count rate after 8 days? Show your working.

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8. Complete the nuclear equation for alpha decay of radon:
$_{86}^{222}\text{Rn} \rightarrow \, _{84}^{218}\text{Po} + \text{ ?}$
Write the missing particle.

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9. Explain why beta particles are negatively charged electrons even though they come from the nucleus.

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10. A sheet of paper can stop alpha particles but not beta particles. State one material that can stop beta particles and one that can stop gamma rays.
Beta stopper: ____________________
Gamma stopper: ____________________

11. The diagram shows a radiation detector near a source.

Image pending generation: diagram for Q11.

If the count rate drops sharply when the aluminium is inserted, what type of radiation was mainly emitted? Give a reason.

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12. State the charge and mass (relative to proton) of an alpha particle.
Charge: ____________
Mass: ____________

13. A sample has $1.2 \times 10^{20}$ unstable nuclei. After 3 half-lives, how many remain? Show working.

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14. Give one reason why handling radioactive sources requires lead-lined containers.

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15. Background radiation comes from natural and artificial sources. Name one natural and one artificial source.
Natural: ____________________
Artificial: ____________________

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Section C: Extended Responses (3 marks each)

16. Describe an experiment to measure the half-life of a radioactive source using a GM tube and counter. Include the steps and how the half-life is found from the data.

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17. Compare the penetrating power and ionising ability of alpha, beta, and gamma radiation. Use a table or clear sentences.

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18. A source has an initial activity of 1200 Bq and a half-life of 2 hours. Calculate the activity after 6 hours. Show your working and state the unit.

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19. Explain how a smoke detector uses a small alpha source to detect smoke. Why is alpha suitable for this use?

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20. Nuclear fission of uranium-235 releases energy. Describe what happens in a fission reaction and why it can continue as a chain reaction.

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

Total Marks: 40
Topic: Modern Physics (Radioactivity / nuclear model)
Note: Content generated from syllabus-first LLM templates (Stage 4/5). Past-paper evidence for this topic was very weak (0.2% of corpus); this quiz is NOT claimed to be exam-derived.

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Section A: Multiple-Choice (1 mark each)

1. C – Gamma ray.
Teaching note: Gamma rays are electromagnetic waves (photons) with no rest mass and no charge. Alpha = 2 protons + 2 neutrons (charge +2). Beta = electron (charge –1). Proton is a nucleon, not a radiation type here.

2. B – half the nuclei present to decay.
Teaching note: Half-life is defined as the time for the activity (or number of undecayed nuclei) to fall to half its initial value. Not all decay at once.

3. B – Beta.
Teaching note: Charged particles deflect in magnetic fields. Beta (electron, low mass, charge –1) deflects more than alpha (heavy, charge +2) and gamma (no charge) does not deflect.

4. B – 146.
Method: Neutrons = mass number – proton number = 238 – 92 = 146.

5. B – Using gamma rays to sterilise medical equipment.
Teaching note: Gamma sterilisation is a safe controlled industrial use. Radium paint and food irradiation for flavour are not safe/approved everyday uses at O-Level.

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Section B: Structured Short Answers (2 marks each)

6. [1 mark each]
Alpha: positively charged, heavy, low penetration, high ionising. (any one)
Gamma: no charge/mass, high penetration, low ionising. (any one)

7. Half-life = 4 days; 8 days = 2 half-lives.
After 1st: 800 ÷ 2 = 400 counts/s
After 2nd: 400 ÷ 2 = 200 counts/s
Answer: 200 counts/s [2 marks: 1 for 2 half-lives, 1 for correct value]

8. Missing particle is alpha: $_{2}^{4}\text{He}$ (or $\alpha$).
Check: 222 = 218 + 4; 86 = 84 + 2. [2 marks]

9. Beta particles are electrons emitted when a neutron in the nucleus changes into a proton and an electron:
$n \rightarrow p + e^{-} + \bar{\nu}$. The electron is ejected from the nucleus. [2 marks]

10. Beta stopper: aluminium (few mm). Gamma stopper: thick lead/concrete. [1+1]

11. Mainly beta radiation.
Reason: Aluminium stops alpha but not beta; sharp drop means beta was being blocked. [1+1]
Image note: Source→aluminium→GM tube; with aluminium, count drops → beta.

12. Charge: +2 (or +2e). Mass: 4 (approx 4 × proton). [1+1]

13. After 3 half-lives, fraction remaining = $(1/2)^3 = 1/8$.
Remaining = $1.2 \times 10^{20} \div 8 = 1.5 \times 10^{19}$. [2 marks]

14. Lead absorbs gamma and reduces exposure; protects user from radiation. [2 marks]

15. Natural: cosmic rays / rocks / radon gas. Artificial: medical X-rays / nuclear tests. [1+1]

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Section C: Extended Responses (3 marks each)

16. [3 marks]

• Place source at fixed distance from GM tube, record counts over time intervals. (1)
• Subtract background count, plot activity vs time. (1)
• Find time for count to halve repeatedly; average gives half-life. (1)

17. [3 marks]
Alpha: least penetration (paper), most ionising.
Beta: medium (aluminium), medium ionising.
Gamma: most penetration (lead), least ionising. (1 mark each)

18. 6 h = 3 half-lives (2 h each).
Activity = $1200 \times (1/2)^3 = 1200 \div 8 = 150$ Bq. [2 for working, 1 for unit/answer]
Answer: 150 Bq

19. [3 marks]
Smoke detector has Am-241 alpha source ionising air between plates, causing small current. (1) Smoke enters, absorbs alpha, current drops, alarm sounds. (1) Alpha suitable: short range, safe if enclosed, strong ioniser. (1)

20. [3 marks]
U-235 absorbs neutron, splits into two smaller nuclei + 2–3 neutrons + energy. (1) Released neutrons cause further fissions. (1) If each fission releases enough neutrons to sustain next, chain reaction continues. (1)