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
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- understand the equivalence between energy and mass as represented by E = mc2 and recall and use this equation
- represent simple nuclear reactions by nuclear equations of the form N He O H
- define and use the terms mass defect and binding energy
- sketch the variation of binding energy per nucleon with nucleon number
- explain what is meant by nuclear fusion and nuclear fission
- explain the relevance of binding energy per nucleon to nuclear reactions, including nuclear fusion and nuclear fission
- calculate the energy released in nuclear reactions using E = c2∆m
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.
- › Recall that in β+ decay, a proton changes into a neutron and emits a positron and a neutrino.
- › When asked for the origin of a particle in decay, describe the specific quark or nucleon change occurring.
- › In beta-plus decay, a proton turns into a neutron, meaning the proton number decreases by one while the nucleon number remains unchanged.
- › Recall that in beta-minus decay, an electron and an antineutrino are emitted; ensure nucleon and proton numbers balance precisely.
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 * c² = 0.005 u * (931.5 MeV/c²) / u * c² = 4.6575 MeV. Therefore, the binding energy is 4.6575 MeV.
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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