← ⚛️ Physics · usually met in Std 9-12
Energy released when atomic nuclei split or join. The amounts are enormous because a tiny amount of mass becomes energy, and the exchange rate is the speed of light squared.
Fission splits a heavy nucleus such as uranium into lighter ones, releasing energy and more neutrons, which can split further nuclei — a chain reaction. A power station controls that chain carefully; a weapon does not. Fusion joins light nuclei, usually hydrogen, into heavier ones, and releases even more energy. Fusion is what powers the Sun and every other star.
The reason the numbers are so large is Einstein's relation between mass and energy: the products weigh very slightly less than what went in, and that missing mass reappears as energy multiplied by an enormous factor. The difficulty with fission is the waste, which stays dangerous for a very long time. The difficulty with fusion is that making it work on Earth requires conditions found inside stars, and after seventy years of research it still consumes more than it returns.
Want to see it moving? Search YouTube for “Nuclear energy” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.
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