| English | Mass defect |
|---|---|
| Bahasa Melayu | Cacat jisim |
| 中文 | 质量亏损 |
Definition
The difference between the total mass of the separate nucleons and the mass of the nucleus they form, which is released as energy.
In exam terms
Mass defect is the difference between the total mass of the separate nucleons (protons and neutrons) and the actual mass of the nucleus they form. It is a mass, symbol Δm, measured in kilograms (kg) or atomic mass units (u).
The 'missing' mass is not lost; it is released as energy when the nucleus forms, according to E = mc². A correct exam sentence: The mass of the assembled nucleus is less than the sum of its nucleons; this mass defect Δm is converted into the binding energy of the nucleus. The larger the mass defect per nucleon, the more tightly bound and stable the nucleus.
Do not confuse it with…
Do not confuse mass defect with binding energy. Mass defect is the missing mass (in kg); binding energy is the energy equivalent of that mass, E = Δmc² (in J).
One is a mass, the other is an energy, they are linked by E = mc² but are not the same quantity.
In Paper 2 this appears as define mass defect, or calculate the mass defect then the energy released. In a calculation, find Δm = (total mass of nucleons − mass of nucleus) in kg first, then multiply by c² = (3.0 × 10⁸)² to get energy in J.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)