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Concept · Modern Physics
Mass-energy & binding energy
E=mc2, mass defect and binding energy, energy release in fission/fusion, recoil via momentum conservation
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Named traps
9 ways this goes wrong.
Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.
- BE per nucleon vs stability reversedAssociates higher binding energy per nucleon with less stability.→
- Binding energy adds massBelieves binding energy adds mass to the nucleus rather than corresponding to the missing mass defect.→
- E=mc2 drops the squareUses E=mc instead of E=mc2, omitting the squaring of the speed of light.→
- Energy from total mass not defectComputes released energy from the total nuclear mass rather than the small mass change/defect.→
- Fusion energy for heavy nucleiThinks fusion of heavy nuclei (or fission of light nuclei) releases energy, ignoring the iron-peak trend.→
- Mass defect sign reversedTakes the nucleus mass as larger than its separate nucleons, reversing the mass defect.→
- Recoil energy split equallySplits the released energy equally between the heavy daughter and light emitted particle, ignoring that the lighter particle carries far more kinetic energy.→
- Recoil ignores momentum conservationFinds a decay product's recoil speed without setting the daughter and emitted particle momenta equal and opposite from a nucleus at rest.→
- Total vs per-nucleon BE confusedCompares total binding energies to judge stability instead of binding energy per nucleon.→
Key formulas
No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.
Shaky underneath?
If the concept underneath still feels loose, patch it here before coming back to CSCA questions.
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