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A2 · Topic 23

The mass that becomes energy.

Mass defect and binding energy through E = mc², the binding-energy-per-nucleon curve that explains fusion and fission, and the random, exponential law of radioactive decay. Play the two simulations below. The gamified lessons and the topic Paper 4 practice are live below too.

Simulations · live
Interactive · live Binding energy per nucleon Slide along the curve from hydrogen to uranium, find the iron peak, and see why fusion and fission both release energy. Loads only when you launch, so the page stays fast.
Interactive · live Radioactive decay Watch individual nuclei decay at random while the count traces a smooth exponential, halving every half-life. Loads only when you launch, so the page stays fast.
Paper 4 practice · live
Structured questions · with worked solutions Ten original Paper 4 style questions A full topic set across mass defect, binding energy, E = mc² and radioactive decay, linking the lessons with full worked solutions. Open practice →
Lessons · live
Mass defect and binding energy → Radioactive decay →
Concept map
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