Chapter 13 of Class 12 Physics – Nuclei – takes you deep into the core of atoms and helps you understand how nuclear forces work. It discusses the size and composition of nuclei, nuclear binding energy, radioactive decay, fission, fusion and basic nuclear reactions. This chapter is very important to understand how energy is produced in nuclear power plants and also how nuclear weapons work. Whether you’re aiming for board exams or competitive ones, this chapter carries a lot of weight.
I chose to write about this chapter because it’s one of those topics that directly connects classroom physics to the real world. Nuclear power, radiation in medical treatment, atomic clocks and even smoke detectors – all are based on principles from this chapter. Many students find it difficult at first because of the formulas and conceptual depth, but if explained with simple logic, it becomes very interesting. I’ve personally seen how learning this chapter well helps in mastering topics in modern physics, especially for exams like NEET and JEE. Having the NCERT PDF handy makes it easier to revise during travel or just before a test.
What You’ll Learn in NCERT Chapter 13: Nuclei
This chapter is all about what’s inside the nucleus and how it behaves. It builds on the previous chapter (Atoms) and gives a deeper view of atomic structure.
Composition of Nucleus
- Nucleus is made of protons and neutrons (together called nucleons)
- Proton number = atomic number (Z)
- Mass number = Z + N (where N is number of neutrons)
Nuclear Mass and Binding Energy
Nuclear mass is always less than the total mass of nucleons
- The difference in mass is called mass defect
- This mass defect is converted to energy, known as binding energy
Binding energy formula:
Eb=(Δm)c2E_b = (\Delta m)c^2Eb=(Δm)c2
where Δm\Delta mΔm is mass defect and ccc is speed of light
Nuclear Force
- Extremely strong force that binds protons and neutrons inside the nucleus
- Short range (effective only within 1-2 fm)
- Attractive in nature and stronger than electrostatic repulsion between protons
Radioactivity
Some nuclei are unstable and spontaneously decay
- Alpha decay: emits 2 protons + 2 neutrons (Helium nucleus)
- Beta decay: neutron converts to proton or vice versa, releasing an electron or positron
- Gamma decay: emission of high-energy photon after alpha or beta decay
Nuclear Fission and Fusion
- Fission: A heavy nucleus splits into smaller ones, releasing energy. Used in nuclear reactors.
- Fusion: Two light nuclei combine to form a heavier nucleus. Happens in the sun and hydrogen bombs.
Download PDF – NCERT Class 12 Physics Chapter 13
For students looking to download the official NCERT PDF, here’s how to get it easily:
