Teacher Demonstration
Use the live model as a shared screen demonstration before students try their own predictions and observations.
Physics / Modern Physics
Three State Decay Theory
Explore Three State Decay Theory as an interactive EJS simulation for modern physics.
1. Watch or Launch
Launch the Interactive
Open the simulation, adjust the controls, and compare what changes on screen before answering the concept-check questions.
2. Big Ideas
Key idea Radioactive decay models show statistical change in a population of nuclei. The meaningful evidence is the number remaining, activity or graph shape, half-life, and the randomness of individual decay events.
What Students Can Learn
- Read the undecayed count or activity against time.
- Connect half-life to a population falling by half, not a fixed decay time for each nucleus.
- Use dice or repeated trials to discuss randomness and sample size.
- Compare parent, intermediate, and daughter populations in three-state models.
Guiding Question
How does the displayed count or activity change over time, and what does that show about half-life and random decay?
3. Try the Investigation
Record the Starting Population
Note the initial number of nuclei, dice, or parent atoms before running the model.
Run One Interval
Observe how many decay events occur and how many undecayed nuclei remain.
Compare Several Intervals
Use the graph or counts to see whether the population falls in a half-life pattern.
Discuss Randomness
Compare repeated runs or dice trials to separate random individual events from the overall decay trend.
4. Teacher Notes
Lesson Use
Use this as a probability-and-population lesson. Ask students to explain why individual decay is unpredictable but the population trend can still be modelled.
Discussion Prompts
Ask: What halves during one half-life? Why do repeated dice runs differ? How does a larger sample make the decay curve smoother?
Teaching Moves
Have students annotate the graph at successive half-lives and describe the surviving fraction. For dice pages, compare two runs before discussing expected behaviour.
Model Notes
Target the displayed count, activity, graph shape, and dice/random trial mechanism. Avoid only saying 'radioactivity decreases' without time and population evidence.
5. Concept Check
These questions are generated from the topic and the concept illustrated by the simulation. Use them after students have explored the model.
Concept Score
Correct first attempts build a streak and unlock higher point multipliers on this device.
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Answer each question once to build your streak.
1. What should come with a measured value?
2. Why choose a suitable instrument?
3. What does uncertainty remind us?
4. Why repeat a measurement?
5. What is a good measurement explanation?
Expert Challenge
Unlocks after 3 correct concept-check answers on this page.
1. In a radioactive-decay interactive, what should students compare as time passes?
2. What feedback fits 'half-life means all nuclei decay exactly halfway through the run'?
3. How should students use the dice-decay model?
4. What should students check in a three-state decay model?
5. What makes a nuclear-decay answer expert-level?
7. Learning Pulse
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