Nuclear Fusion
Fusion combines light nuclei. Its Q value is obtained from mass difference or total-binding difference; a positive value is released as product kinetic energy or radiation. High temperature raises collision energies but quantum tunnelling also matters.
Why this shows up in the exam
Stellar energy generation · Deuterium-tritium reaction calculations · Computing energy from a macroscopic fuel mass
Learn the idea
Fusion releases energy when light nuclei combine into products with greater total binding energy. Light nuclei lie on the rising side of the binding-energy curve. Joining them can move nucleons into a more tightly bound arrangement, but positively charged nuclei must first approach through the Coulomb barrier.
🧠 Memory hook: Light nuclei climb the binding curve by joining.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- Q_fusion = B_products - B_reactants — released energy when the total product binding is larger
- N_reactions = sample mass / (molar mass) times N_A — reaction-count estimate when every specified fuel nucleus is consumed
How to approach it
- 1Balance the fusion equation
- 2Compute total binding before and after
- 3Multiply per-reaction energy by the actual reaction count
Common slip-ups that cost marks
- •Adding B/A values without multiplying by nucleon counts
- •Ignoring the Coulomb barrier
- •Calling every combination of nuclei exothermic
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
In hydrogen, an electron transitions from n = 2 to n = 1. Using E_n = -13.6/n^2 eV, find the emitted photon energy.
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