Chapter 09WBCHSE BoardClass XIIPhysics
Atoms & Nuclei
পরমাণু ও নিউক্লিয়াস
Rutherford alpha scattering, Bohr's postulates for hydrogen atom, energy levels and hydrogen spectral series, mass defect, binding energy curve, and nuclear fission and fusion.
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Syllabus Reference Module
Target Learning Objectives
- Apply Bohr's quantization postulate: L = mvr = nh / 2π.
- Derive expressions for radius, velocity, and total energy of electron in nth Bohr orbit.
- Calculate wavelengths of Lyman, Balmer, Paschen spectral series using Rydberg formula.
- Calculate nuclear mass defect and binding energy per nucleon.
Governing Physical Concepts
- Rutherford Distance of Closest Approach
- Bohr Hydrogen Atom Radii (r_n = 0.529 n^2 / Z Å)
- Energy Levels: E_n = -13.6 Z^2 / n^2 eV
- Rydberg Formula: 1/λ = R Z^2 (1/n1^2 - 1/n2^2)
- Mass Defect (Δm) & Einstein Mass-Energy Equivalence (E = Δm c^2)
- Nuclear Binding Energy per Nucleon Curve & Stability
Structured Concept Hierarchy
Chapter Topics & Breakdown
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Academic Library
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Quick Revision Summary
“Balmer series lines fall in the visible spectrum; Lyman falls in the ultraviolet region.”
- •Binding energy per nucleon peaks around Iron (A ≈ 56 at ~8.75 MeV), explaining fission and fusion energy release.
- •Nuclear density is constant for all nuclei (~2.3 × 10^17 kg/m^3), independent of mass number A.
- •Total energy in Bohr orbit is negative: E = -K = U/2.
Structured Practice Roadmap
Spectral series wavelength transitions, Bohr orbit calculations, and nuclear binding energy mass defect.
Problem Bank Volume:24 Selected Problems
Problem Categories:
Bohr Transition WavelengthsBinding Energy per NucleonRydberg Calculations
Board Diagnostic 09: Modern Physics I
Assessment Architecture • Academic Evaluation SpecificationWritten paper on atomic spectra and nuclear binding energy.
FormatWritten Board Paper
Duration50 Minutes
Coverage18 Questions
* Note: Written assessments are administered and reviewed directly by faculty. Digital diagnostic assessment engines are scheduled for subsequent platform phases.