Chapter 13.5 Nuclear Force 🤝

Inside every nucleus, protons and neutrons (collectively nucleons) stick together because of a special glue called the nuclear force. This force has nothing to do with the usual electric or gravitational pulls you meet in everyday life — it is far stronger and acts only over tiny distances. 💡 Think of it like Velcro that works only when hooks and loops are almost touching. :contentReference[oaicite:0]{index=0}

Main Features at a Glance ✨

  • Super-strong 💪 – It easily beats the repulsive Coulomb push between positively charged protons and dwarfs gravity. :contentReference[oaicite:1]{index=1}
  • Short-range ⚡ – Its grip dies out rapidly once nucleons are separated by more than a few femtometres (1 fm = 10-15 m). This “reach limit” explains why each nucleon mainly talks to its closest neighbours (the saturation property). :contentReference[oaicite:2]{index=2}
  • Distance sweet-spot 💖 – The potential energy between two nucleons touches a minimum at \(r_0 \approx 0.8\;\text{fm}\).
    • For separations greater than \(r_0\): the force is attractive.
    • For separations smaller than \(r_0\): the force flips and becomes strongly repulsive, preventing the nucleus from collapsing in on itself. :contentReference[oaicite:3]{index=3}
  • Charge-independent 🟰 – Whether you pair neutron-neutron, proton-neutron, or proton-proton, the nuclear force behaves almost the same. It doesn’t care about electric charge. :contentReference[oaicite:4]{index=4}
  • No simple formula 📈 – Unlike Coulomb’s neat \(1/r^{2}\) law, the nuclear force cannot be captured by a single tidy equation. Physicists map it experimentally instead. :contentReference[oaicite:5]{index=5}

Energy Connections 🔗

Average-mass nuclei sit at a binding-energy “plateau” of about \(E_{bn} \approx 8\;\text{MeV per nucleon}\). Two big pay-offs follow: :contentReference[oaicite:6]{index=6}

  1. Fission ⚡ – A very heavy nucleus (say \(A=240\)) splits into two medium ones (\(A≈120\)). The products have higher binding energy per nucleon, so energy is released. This principle powers nuclear reactors. :contentReference[oaicite:7]{index=7}
  2. Fusion ☀️ – Very light nuclei (\(A≤10\)) merge into a heavier nucleus with a larger \(E_{bn}\). That surplus in binding energy appears as the Sun’s radiant power. :contentReference[oaicite:8]{index=8}

Quick Equations 🧮

  • Binding-energy plateau: \(E_{bn} \approx 8\;\text{MeV}\)
  • Range marker: \(r_0 \approx 0.8\;\text{fm}\)

High-Yield Ideas for NEET 🚀

  1. Nuclear force strength vs. Coulomb force — explains how nuclei overcome proton repulsion.
  2. Short-range & saturation — key for understanding binding-energy curves.
  3. Charge independence — identical behaviour for nn, pn, pp pairs.
  4. Attractive-then-repulsive profile — minimum at \(r_0\) safeguards nuclear size.
  5. Energy release through fission and fusion — direct link to real-world power generation.

😊 Keep these points handy — they pop up often in NEET physics questions!