Mass defect and nuclear binding energy
Cambridge A-Level Physics (9702) · Unit 23: Nuclear physics · 9 flashcards
Mass defect and nuclear binding energy is topic 23.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 23 — Nuclear physics , alongside Radioactive decay. In one line: E = mc², where E is energy (J), m is mass (kg), and c is the speed of light in a vacuum (approximately 3.00 x 10⁸ m/s). This equation shows that mass can be converted into energy and vice-versa.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 9 flashcards — 4 definitions, 4 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 4 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Einstein's mass-energy equivalence equation and define each term
E = mc², where E is energy (J), m is mass (kg), and c is the speed of light in a vacuum (approximately 3.00 x 10⁸ m/s). This equation shows that mass can be converted into energy and vice-versa.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Understand that mass and energy are equivalent, as shown by E = mc², and be able to recall this equation and use it.
- Use nuclear equations such as ¹⁴₇N + ⁴₂He → ¹⁷₈O + ¹₁H to represent simple nuclear reactions.
- Define binding energy and mass defect, and use both terms.
- Sketch a graph showing how binding energy per nucleon changes with nucleon number.
- Explain what nuclear fission and nuclear fusion are.
- Explain how binding energy per nucleon relates to nuclear reactions, including fission and fusion.
- Use E = c²Δm to calculate how much energy a nuclear reaction releases.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Mass defect and nuclear binding energy
- › Specify that nucleons must be separated to infinity when defining binding energy.
- › In nuclear reactions, recognize that a decrease in total mass corresponds to the release of energy according to E = mc^2.
State Einstein's mass-energy equivalence equation and define each term.
E = mc², where E is energy (J), m is mass (kg), and c is the speed of light in a vacuum (approximately 3.00 x 10⁸ m/s). This equation shows that mass can be converted into energy and vice-versa.
Define 'mass defect' in the context of nuclear physics.
Mass defect (Δm) is the difference between the mass of the individual nucleons (protons and neutrons) in a nucleus and the actual mass of the nucleus. This 'missing' mass is converted into binding energy.
Define 'nuclear binding energy'.
Nuclear binding energy is the energy required to separate a nucleus into its constituent protons and neutrons. It is equivalent to the mass defect via E=mc².
Describe the general trend of binding energy per nucleon with increasing nucleon number (A).
Binding energy per nucleon increases sharply for light nuclei, reaches a maximum around A=56 (Iron, Fe), and then slowly decreases for heavier nuclei. This trend dictates the energy release during fusion and fission.
Explain the process of nuclear fusion.
Nuclear fusion is the process where two light nuclei combine to form a heavier nucleus. This process releases energy when the resulting nucleus has a higher binding energy per nucleon than the original nuclei (
Explain the process of nuclear fission.
Nuclear fission is the process where a heavy nucleus splits into two or more lighter nuclei. This process releases energy when the resulting nuclei have a higher binding energy per nucleon than the original nucleus (
Explain the relevance of binding energy per nucleon to nuclear reactions.
Nuclear reactions release energy if the binding energy per nucleon of the products is greater than that of the reactants. This is why fusion releases energy for light nuclei, and fission releases energy for heavy nuclei.
A nucleus has a mass defect of 0.005 u. Calculate the binding energy in MeV (Mega electron volts). (1 u = 931.5 MeV/c²)
Binding energy = Δm × 931.5 MeV per u = 0.005 × 931.5 MeV ≈ 4.7 MeV (about 5 MeV to the 1 significant figure of the data).
Write a balanced nuclear equation representing the alpha decay of Uranium-238 (²³⁸U).
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He. This equation shows Uranium-238 decaying into Thorium-234 and an alpha particle (Helium-4 nucleus).
Review the material
Read full revision notes on Mass defect and nuclear binding energy — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 23 — Nuclear physics
Mass defect and nuclear binding energy sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Mass defect and nuclear binding energy deck
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