An Overview of Ncert Books Class 12 Physics Chapter 13 Free Download
FAQs on Ncert Books Class 12 Physics Chapter 13 Free Download
1. What are the most frequently asked 3-mark and 5-mark questions from Chapter 13, Nuclei, for the CBSE Class 12 Board Exam 2025-26?
For the CBSE Class 12 Physics exam, questions from the Nuclei chapter are structured to test both theoretical and numerical understanding. Based on board trends, here are some expected types:
3-Mark Questions: These often involve derivations like the law of radioactive decay (N = N₀e⁻ˡᵗ), numerical problems on half-life and mean life, or explaining the properties of alpha, beta, and gamma radiation.
5-Mark Questions: A very important 5-mark question is to draw the binding energy per nucleon vs. mass number curve and explain its key features, including the implications for nuclear fission and fusion. Another expected question could be on the principle and working of a nuclear reactor with a labelled diagram.
2. Which topics from the NCERT textbook for Nuclei are crucial for scoring well in the board exams?
To score well, a thorough understanding of the NCERT textbook is essential. For the Nuclei chapter, the most important topics as per the CBSE 2025-26 syllabus are:
Composition and Size of the Nucleus: Focus on the relationship between radius and mass number.
Mass-Energy Relation and Mass Defect: Understand Einstein's mass-energy equivalence and how to calculate mass defect.
Binding Energy Curve: This is a very high-yield topic. Understand its shape, the peak, and what it implies about nuclear stability.
Nuclear Fission and Fusion: Know the basic reactions and the energy released in each process.
Radioactivity: The law of radioactive decay, half-life, and mean life are crucial for numerical problems.
3. What types of numerical problems are important from the Nuclei chapter?
The Nuclei chapter is numerically intensive. Important question types for the exam include:
Calculating mass defect (Δm) and then finding the binding energy (BE) of a nucleus using the formula BE = Δmc².
Problems based on the radioactive decay law, where you might need to find the amount of substance remaining after a certain time, or calculate the decay constant (λ).
Calculating the half-life (T₁/₂) or mean life (τ) of a radioactive sample.
Determining the energy released (Q-value) in a nuclear fission or fusion reaction.
Practising these types thoroughly is key to securing good marks.
4. How does the concept of mass defect and binding energy explain the stability of a nucleus?
This is a high-order thinking skill (HOTS) question. The stability of a nucleus is directly explained by its binding energy per nucleon. The mass of a stable nucleus is always less than the sum of the masses of its constituent protons and neutrons. This difference in mass, called the mass defect (Δm), is converted into energy (binding energy) that holds the nucleons together, as per Einstein's equation E = Δmc². A higher binding energy per nucleon signifies that more energy is required to break the nucleus apart, making it more stable.
5. Why is the Nuclei chapter often considered difficult, and what is its approximate weightage in the board exam?
Students often find the Nuclei chapter challenging due to its abstract concepts and the number of formulas related to radioactivity, mass-energy equivalence, and binding energy. The questions often require both strong conceptual clarity and precise calculation skills. In the CBSE Class 12 Physics paper, the unit 'Atoms and Nuclei' together holds significant weightage, typically around 12 marks. The Nuclei chapter itself contributes substantially to this, making it too important to ignore.
6. What is the fundamental difference between nuclear fission and nuclear fusion, and why are questions on this topic important?
This is a classic and important distinction. The key differences are:
Process: Nuclear Fission is the process where a heavy, unstable nucleus (like Uranium-235) splits into two or more lighter nuclei. Nuclear Fusion is the process where two light nuclei (like hydrogen isotopes) combine to form a heavier nucleus.
Conditions: Fission can occur at normal temperatures and pressures. Fusion requires extremely high temperatures and pressures to overcome the electrostatic repulsion between the positively charged nuclei.
Energy Release: While a single fusion event releases less energy than a single fission event, the energy released per nucleon is much greater in fusion.
Questions on this topic are important because they test a student's understanding of the binding energy curve and its real-world applications, such as in nuclear reactors (fission) and stars (fusion).
7. What are some expected 1-mark questions or MCQs from the Nuclei chapter for the 2025-26 exam?
For the one-mark section, expect direct, concept-based questions. Important examples include:
Defining terms like isotopes, isobars, and isotones with one example.
Stating the relationship between the radius of a nucleus (R) and its mass number (A), i.e., R ∝ A¹/³.
What is the SI unit of radioactivity or activity? (Becquerel, Bq).
Identifying the particle emitted in a given nuclear decay equation (alpha or beta decay).
8. Are questions on the properties of nuclear forces important for the CBSE board exam?
Yes, questions on the properties of nuclear forces are frequently asked, usually for 2 or 3 marks. It is important to remember the key characteristics. You should be prepared to list and briefly explain that nuclear forces are:
The strongest forces in nature.
Short-ranged, acting only within the dimensions of the nucleus.
Charge-independent, meaning the force between a proton-proton, neutron-neutron, and proton-neutron is nearly the same.
Saturated forces, meaning a nucleon interacts only with its immediate neighbours.
