Half-Life — GCSE Physics Revision
Revise Half-Life for GCSE Physics. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to Nuclear Fission & FusionWhat is Half-Life?
The half-life of a radioactive isotope is the time it takes for the number of unstable nuclei in a sample to halve, or the time it takes for the activity (the number of decays per second) of the sample to fall to half its initial value. It is a constant value for a given isotope and is not affected by external factors.
Board notes: A Higher Tier topic for all major GCSE Physics boards (AQA, Edexcel, OCR). You will be expected to perform calculations and interpret decay graphs.
Step-by-step explanationWorked example
A radioactive sample has an initial activity of 800 Bq. Its half-life is 10 minutes. What will its activity be after 30 minutes? Solution: 30 minutes is three half-lives (30/10 = 3). After 1 half-life: 400 Bq. After 2 half-lives: 200 Bq. After 3 half-lives: 100 Bq.
Mini lesson for Half-Life
1. Understand the core idea
The half-life of a radioactive isotope is the time it takes for the number of unstable nuclei in a sample to halve, or the time it takes for the activity (the number of decays per second) of the sample to fall to half its initial value. It is a constant value for a given isotope and is not affected by external factors.
Can you explain Half-Life without copying the notes?
2. Turn it into marks
A radioactive sample has an initial activity of 800 Bq. Its half-life is 10 minutes.
Underline the method, evidence, or command-word move that would earn credit in GCSE Atomic Structure.
3. Fix the likely mark leak
Watch for this mistake: Thinking that after two half-lives, the activity will be zero. It will be a quarter of the original activity (half of a half).
Write one correction rule before doing another practice question.
Practise this topic
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Half-Life practice questions
These are original StudyVector questions for revision practice. They are not official exam-board questions.
Question 1
In one GCSE sentence, explain what Half-Life is testing.
Answer: The half-life of a radioactive isotope is the time it takes for the number of unstable nuclei in a sample to halve, or the time it takes for the activity (the number of decays per second) of the sample to fall to half its initial value. It is a constant value for a given isotope and is not affect...
Mark focus: Precise definition and topic focus.
Question 2
A Half-Life question uses an unfamiliar context. What should the answer do before adding detail?
Answer: It should name the process, variable, equation, particle model, or evidence being tested, then explain the result using precise scientific vocabulary.
Mark focus: Method selection and command-word control.
Question 3
A student makes this mistake: "Thinking that after two half-lives, the activity will be zero. It will be a quarter of the original activity (half of a half)." What should their next repair task be?
Answer: Do one Half-Life question and review the mistake type.
Mark focus: Error correction and next-step practice.
Half-Life flashcards
Core idea
What is the main idea in Half-Life?
The half-life of a radioactive isotope is the time it takes for the number of unstable nuclei in a sample to halve, or the time it takes for the activity (the number of decays per second) of the sample to fall to half...
Common mistake
What mistake should you avoid in Half-Life?
Thinking that after two half-lives, the activity will be zero. It will be a quarter of the original activity (half of a half).
Practice
What is one useful practice task for Half-Life?
Answer one Half-Life question and review the mistake type.
Exam board
How should you use board notes for Half-Life?
A Higher Tier topic for all major GCSE Physics boards (AQA, Edexcel, OCR). You will be expected to perform calculations and interpret decay graphs.
Common mistakes
- 1Thinking that after two half-lives, the activity will be zero. It will be a quarter of the original activity (half of a half).
- 2Calculating the half-life incorrectly from a graph. You must find the time taken for the activity to fall to half of its starting value.
- 3Confusing half-life with the lifetime of a single nucleus. Half-life is a statistical measure for a large number of nuclei.
Half-Life exam questions
Exam-style questions for Half-Life with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Half-Life
Core concept
The half-life of a radioactive isotope is the time it takes for the number of unstable nuclei in a sample to halve, or the time it takes for the activity (the number of decays per second) of the sampl…
Frequently asked questions
How is half-life used in radioactive dating?
Carbon-14 is a radioactive isotope with a half-life of about 5730 years. By measuring the amount of Carbon-14 remaining in an ancient organic object, scientists can determine its age.
Why are isotopes with short half-lives used in medical tracers?
Isotopes with short half-lives are used so that they decay quickly and do not remain in the patient's body for a long time, minimizing the radiation dose and potential harm.