Nuclear Energy — A-Level Physics Revision

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What is Nuclear Energy?

This topic explores how energy can be released from the nucleus of an atom, based on Einstein's principle of mass-energy equivalence (E=mc²). It covers the two main processes: nuclear fission, the splitting of a large, unstable nucleus (like Uranium-235) into smaller nuclei, and nuclear fusion, the joining of two light nuclei to form a heavier nucleus. You will study the concept of binding energy per nucleon and how it explains the energy released in these reactions.

Board notes: Nuclear fission and fusion are key topics in all A-Level Physics specifications (AQA, Edexcel, OCR). All boards expect an understanding of mass defect, binding energy, and the application of E=mc². The principles of a thermal nuclear reactor, including the roles of the moderator and control rods, are also a common requirement.

Worked example

Common mistakes

• 1Confusing fission and fusion. Fission is the splitting of a heavy nucleus, while fusion is the joining of light nuclei. A simple mnemonic is that 'fusion' sounds like 'fuse', meaning to join together.
• 2Misinterpreting the binding energy curve. The peak of the curve (around iron) represents the most stable nuclei. Energy is released when moving towards the peak, either by splitting very heavy nuclei (fission) or joining very light nuclei (fusion).
• 3Thinking that mass is lost in nuclear reactions. Mass and energy are inter-convertible. In an exothermic nuclear reaction, a small amount of mass (the mass defect) is converted into a large amount of energy according to E=mc².

Nuclear Energy exam questions

Exam-style questions for Nuclear Energy with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is a chain reaction in nuclear fission?

  A chain reaction occurs when the neutrons released from one fission event go on to trigger further fission events in other nuclei. In a nuclear reactor, this process is controlled to produce a steady release of energy.

• Why is it so difficult to achieve nuclear fusion on Earth?

  Fusion requires extremely high temperatures and pressures to overcome the electrostatic repulsion between the positively charged nuclei and force them close enough to fuse. Creating and containing these conditions (a plasma hotter than the sun) is a major technological challenge.