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O Level Physics Modern Physics Quiz

Free O Level Physics Modern Physics quiz, HY3 Exam version, with questions, answers, and O Level-style practice for Singapore students.

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Questions

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.

Section A: Multiple Choice (Questions 1–5)

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

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

Answer: ______
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: ______

Section B: Structured Questions (Questions 6–15)

State one use of gamma rays in medicine. [2]
A radioactive sample has a half-life of 4 hours. Calculate the fraction of the sample remaining after 12 hours. [2]
Working: ______________________________________________________
Answer: ______
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 = ______
Explain why alpha radiation is unsuitable for medical imaging inside the body but suitable for smoke detectors. [2]
A Geiger-Müller tube is used to detect radiation. State what type of radiation it can detect. [2]

The count rate from a source is 800 counts/s. After 2 half-lives, what is the count rate? [2]
Working: ______________________________________________________
Answer: ______ counts/s
State the penetration power of beta particles in order from least to most stopping material. [2]

A sample contains $4.0 \times 10^{12}$ radioactive nuclei. After one half-life, how many remain? [2]
Working: ______________________________________________________
Answer: ______
Give one safety precaution when handling radioactive sources in school labs. [2]

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

Section C: Extended Response (Questions 16–20)

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]

The graph shows the decay of a radioactive isotope.

Graph for 17 (OLEVEL Physics)

Generated 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]

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

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

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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Answers

O-Level Physics Quiz - Modern Physics: Answer Key

Total Marks: 40
Topic: Modern Physics (Radioactivity)

Section A: Multiple Choice

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.
B [1]
Half-life = time for half the radioactive nuclei present to decay. Not all decay at once.
B [1]
Americium-241 emits alpha used in ionization chamber of smoke detectors.
C [1]
Alpha stopped by paper; beta needs aluminium; gamma needs lead.
B [1]
Beta decay: neutron → proton + electron, so atomic number Z increases by 1.

Section B: Structured

[2]
Use: killing cancer cells / tumour treatment (radiotherapy).
Mark: 1 for context, 1 for correct medical use.
[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.
[2]
A = 222 – 4 = 218; Z = 86 – 2 = 84.
Mark: 1 each.
[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.
[2]
Detects alpha, beta, gamma (all ionising radiation).
Mark: 2 for all three, 1 for partial.
[2]
Working: after 1 half-life: 400; after 2: 200.
Answer: 200 counts/s.
Mark: 1 working, 1 answer.
[2]
Paper (alpha) → aluminium (beta) → thick lead (gamma).
Mark: 2 for correct order, 1 partial.
[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.
[2]
Use tongs / store in lead box / limit exposure time.
Mark: 2 for specific, 1 vague.
[2]
Alpha (positive) deflected to negative plate; beta negative to positive. Answer: alpha.
Mark: 2 correct, 1 wrong sign.

Section C: Extended

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