Structured Questions – Half Life

Diagram 3 shows the activity-time graph of radioisotope Potassium-42. This radioisotope emits beta particles and is used as a tracer to measure the quantity of salt in human body.

  1. State one characteristic of beta particles. [1 mark]
    Negatively charged 
  2. Based on Diagram 3 , determine the half-life of Potassium-42. Show on the graph how you determine the half-life of Potassium. [2 mark]
    12 hours
  3. Based on the half life, state why Potassium-42 is suitable to be used as the tracer. [1 mark]
    Potassium-42 has short half-life, hence overexposure does not occur.
  4. Calculate the time taken for radioistope Potassium-42 to reduce \(\frac{1}{8}\) of its initial activity. [2 marks]
    \(1 \underset{ T _{\frac{1}{2}}}{\longrightarrow} \frac{1}{2} \underset{ T _{\frac{1}{2}}}{\longrightarrow} \frac{1}{4} \underset{ T _{\frac{1}{2}}}{\longrightarrow} \frac{1}{8}\)
    The time taken for the activity of the potassium- 42 becomes \(\frac{1}{8}\) of its initial activity.
    &=3 T _{\frac{1}{2}} \\
    &=3 \times 12 \text { hours } \\
    &=36 \text { hours } 

SPM Form 5 Physics Mind Map Formulae List – Chapter 5

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The image above shows the formulae that students need to know in Malaysia SPM Physics syllabus in Mind Map form. You may click on the image to enlarge it for a better view. You may also download and print it out for further reference.

Radioactivity is the last chapter of SPM Form 5 Physics. As you can see, not many formulae in this chapter. For the formula related to half life, usually it is not used to solve the problem because most of the calculation question can be solved by common sense.

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SPM Form 5 Physics Chapter 5 – Radioactivity


  1. The Composition of the Nucleus
  2. Radioactivity
    1. 3 Types of Radioactive Emission
    2. Characteristics of Radioactive Emission
  3. Detectors of Radiation
    1. Gold Leaf Electroscope
    2. Geiger-Muller Tube
    3. Cloud Chamber
    4. Spark-Chamber Detector
    5. Film Badge (Dosimeter)
  4. Radioactive Decay
    1. Alpha Decay
    2. Beta Decay
    3. Gamma Decay
    4. Series Decay
  5. Half-life
  6. Uses of Radioisotopes
    1. Uses of Radioisotope in Archeology
    2. Uses of Radioisotope in Industry
    3. Uses of Radioisotope in Medical
    4. Uses of Radioisotope in Agriculture
  7. Nuclear Energy
    1. Nuclear Fission
      1. Chain Reaction
    2. Nuclear Fusion
    3. Generation of Electricity from Nuclear Fission

Objective Question

  1. Radioactivity (8 Questions)
  2. Radioactive Decay (10 Questions)
  3. Nuclear Energy (5 Questions)