Appreciation that knowledge of the physics of nuclear energy allows…

The idea

Physics does not decide policy, but it supplies the evidence on which sound decisions rest. In nuclear energy, mass–energy equivalence explains why fission releases energy: the products have slightly less mass than the reactants, and the missing mass appears as kinetic energy via ΔE = Δmc². Knowing this lets society compare nuclear power with alternatives on quantities such as energy released per kilogram of fuel, carbon dioxide emissions and radioactive waste.

For example: Calculating the energy from the fission of 1 kg of uranium‑235 shows why a small fuel mass can supply a large city, which informs debate about fuel security and waste storage.

What earns the marks

• State that mass–energy equivalence, ΔE = Δmc², explains the energy released when a nucleus undergoes fission or fusion.
• Explain that the total mass of the products of fission is slightly less than the mass of the original nucleus plus neutron, and this mass difference appears as energy.
• Use quantitative data, such as energy released per kilogram of fuel, to compare nuclear energy with fossil fuels in a decision-making context.
• Describe how scientific evidence about energy release, waste and safety feeds into public and political decisions alongside economic, ethical and environmental considerations.
• Recognise that physics can quantify risks and benefits but cannot by itself settle questions of value or policy.

Common mistakes and how to put them right

• Treating mass as being converted into energy in a vague everyday sense.

  Put it right: A measurable mass difference Δm corresponds to energy ΔE = Δmc².

• Assuming that scientific knowledge automatically determines the best policy.

  Put it right: Decisions also depend on costs, risks, ethics and public values.

• Confusing the energy released per fission with the energy released per kilogram of fuel.

  Put it right: Per-kilogram values require the number of nuclei in the sample, found using Avogadro's constant.

Exam tips

• Link every decision-making point back to a specific physics quantity, such as Δm, ΔE or energy per kilogram, rather than writing general opinions.
• When asked to evaluate, give both a benefit and a limitation of using nuclear energy, and state which evidence supports each.
• Use correct units and powers of ten, for example writing energy in J or MJ kg⁻¹, and keep the mass difference in kg when using ΔE = Δmc².