Simulation of Alpha particle scattering experiment
What the simulation shows
An interactive recreation of the 1909 Geiger–Marsden gold foil experiment. Alpha particles are fired from the left toward a gold atom. A dashed circle shows the atom boundary and electron cloud, with a small dense gold nucleus at the centre marked with a positive charge.
Three colour-coded outcomes appear as particles travel across the canvas — orange trails pass straight through (the majority), red trails deflect at an angle, and gold trails bounce almost directly back. A live counter tracks how many of each type have occurred.
Three modes let students control the rate: Single Shot lets them aim deliberately by clicking at different heights, Burst fires five particles at once across a spread of impact parameters, and Auto runs a continuous weighted stream so the statistics build up in real time.
Suggested class activity — “What does the data tell us?”
Run the simulation in Auto mode for about 30 seconds with the whole class watching. Ask students to observe before explaining anything. Then pause and ask three questions:
- What do most particles do? (Pass straight through — so the atom must be mostly empty space.)
- What happens to the rare ones that go near the centre? (They bounce back — something small and very repulsive is there.)
- Why must that something be positively charged? (Alpha particles carry a positive charge, so only a positive nucleus could repel them back.)
Switch to Single Shot and let individual students take turns clicking at different heights — directly at the nucleus, slightly off-centre, and far out — and predict the outcome before firing. This builds the intuitive link between impact parameter and scattering angle.
Finish with a short written task: “Using the evidence from the simulation, explain why Rutherford concluded that the nucleus is tiny, dense, and positively charged.” This maps directly onto the required GCSE exam response structure — observation, inference, conclusion.