NEB Class 12 Physics Quantization of Energy Notes in PDF Complete Handwritten. Physics Notes 2082: All Chapters | New Curriculum | Class 12 Physics Notes download.
Mero Enotes is a simple educational Website Built to help Class 11 and 12 students excel in their studies. We offer Notes, question papers, and important study materials across various subjects for both science and management faculties. Whether youβre looking for Physics, Chemistry, Biology, Accounting, Economics, and Finance, Mero Enotes provides organized PDF resources, embedded via Google Drive for easy access.
We aim to make studying easier for students by giving them the right materials to prepare for exams.
NEB Class 12 Physics Quantization of Energy Note Handwritten in PDF
$
Bohr’s Model β Four Postulates
- Electrons orbit the nucleus in specific circular orbits (stationary states) without radiating energy
- Only orbits where mvr = nh/2Ο are allowed (angular momentum quantization)
- Energy is emitted or absorbed as photons when electron jumps between orbits: E_photon = hf = E_m β E_n
- The lowest energy orbit (n=1) is the ground state β electron stays here when undisturbed
Derivation of Key Results
Radius of nth orbit: Equating Coulomb force = centripetal force, plus Bohr condition:
r_n = nΒ²aβ where aβ = 0.529 Γ (Bohr radius, ground state radius)
Velocity of electron in nth orbit:
v_n = eΒ²/2Ξ΅βnh = vβ/n (decreases for higher orbits)
Total energy of electron in nth orbit:
E_n = β13.6/nΒ² eV
- Negative sign = electron is bound (energy must be supplied to remove it)
- n=1: E = β13.6 eV (ground state)
- n=2: E = β3.4 eV
- n=3: E = β1.51 eV
- n=β: E = 0 (ionized electron free)
Spectral Series of Hydrogen
When electron jumps from outer orbit nβ to inner orbit nβ (nβ > nβ):
1/Ξ» = R_H (1/nβΒ² β 1/nβΒ²)
Where R_H = 1.097 Γ 10β· mβ»ΒΉ (Rydberg constant)
| Series | Lower level nβ | Region | Notes |
|---|---|---|---|
| Lyman | 1 | Ultraviolet | First series discovered in UV |
| Balmer | 2 | Visible light | 4 visible lines (red, blue-green, blue, violet) |
| Paschen | 3 | Near Infrared | First infrared series |
| Brackett | 4 | Infrared | |
| Pfund | 5 | Far Infrared |
Excitation and Ionization
- Excitation energy: Energy needed to jump electron from ground state to higher level
- 1st excitation energy (n=1 to n=2): 13.6 β 3.4 = 10.2 eV
- 2nd excitation energy (n=1 to n=3): 13.6 β 1.51 = 12.09 eV
- Ionization energy: Energy to remove electron completely from ground state
- For hydrogen: 13.6 eV
De Broglie Hypothesis
Louis de Broglie (1924) proposed: All matter has wave properties
De Broglie wavelength: Ξ» = h/p = h/mv
For an electron:
- At v = 10βΆ m/s: Ξ» β 0.7 nm (comparable to atomic spacing)
- This explains Bohr’s quantization: only orbits where circumference = nΞ» are stable β mvr = nh/2Ο
Wave-particle duality: Both light and matter exhibit both wave and particle properties, depending on the experiment.
Heisenberg Uncertainty Principle: Ξx Β· Ξp β₯ β/2 (more precisely: Ξx Β· Ξp β₯ h/4Ο)
You cannot simultaneously know both position and momentum with perfect precision.
X-rays Production and Properties
Production (Coolidge tube):
- Electrons emitted from hot cathode (tungsten filament)
- Accelerated through high voltage (30β150 kV) toward tungsten anode
- Electrons collide with anode β X-rays produced by two mechanisms:
- Bremsstrahlung (braking radiation): electrons decelerate β emit continuous X-rays
- Characteristic X-rays: electrons knock out inner shell electrons β outer electrons fill in β emit specific frequency X-rays
Properties of X-rays:
- High-energy electromagnetic waves (Ξ» = 0.001 to 10 nm)
- Travel at speed of light
- Not deflected by electric or magnetic fields (no charge)
- Ionize gases
- Penetrate matter (amount depends on material density)
- Cause fluorescence in certain materials
- Affect photographic film
Applications:
- Medical diagnosis (bone X-rays, CT scans)
- Security scanning (airport luggage)
- Crystallography (determining crystal structure)
- Cancer treatment (radiation therapy)
Bragg’s Law X-ray Diffraction
When X-rays strike a crystal, they are reflected from successive parallel planes of atoms.
Condition for constructive interference: 2d sinΞΈ = nΞ»
Where d = interplanar spacing, ΞΈ = glancing angle, n = order, Ξ» = wavelength
Used to:
- Measure wavelength of X-rays (if d is known)
- Determine crystal structure (measure ΞΈ for known Ξ» β find d)
- Discover the double helix structure of DNA (Rosalind Franklin’s X-ray crystallography)
Class 12 Science Faculty All Subject Notes
- Physics Handwritten Notes PDF
- Chemistry Handwritten Notes PDF
- Biology Handwritten Notes PDF
- Nepali Handwritten Notes PDF
- English Handwritten Notes PDF
Student Queries:- Class 12 Physics Notes download | Complete Physics Guide (New Syllabus) | Class 12 Physics Book Solution Guide App | Class 12 Physics Book Notes 2081 Guide | Class 12 Physics All Chapter Notes | Kec Publication Physics class 12 solutions | Neb class 12 physics notes pdf free download | Neb class 11 physics notes handwritten | Class 12 Physics Notes PDF | NEB Class 12 Physics Book PDF | Principle of Physics Class 12 pdf Asmita publication | NEB Class 12 Physics syllabus 2080 | Class 12 Physics Book PDF Nepal 2080
NOTE : βIf you want to download the notes Offline Contact us in Social media β
Frequently Asked Questions
What are Bohr’s postulates in Class 12 Physics?
Four postulates: electrons orbit nucleus in fixed circular orbits without radiating. Only orbits where angular momentum mvr = nh/2Ο are allowed. Energy emitted or absorbed as photon when electron jumps between orbits: E = hf. Ground state (n=1) is the lowest stable energy state of the hydrogen atom.
What is the energy of nth orbit in hydrogen atom Class 12?
Energy of nth orbit: E_n = β13.6/nΒ² eV. Ground state (n=1): β13.6 eV. n=2: β3.4 eV. n=3: β1.51 eV. Negative sign means electron is bound. Ionization energy = 13.6 eV (to remove electron from ground state). Photon energy when electron jumps from nβ to nβ: E = 13.6(1/nβΒ² β 1/nβΒ²) eV.
What are the spectral series of hydrogen atom Class 12?
Wavelength formula: 1/Ξ» = R_H(1/nβΒ² β 1/nβΒ²), R_H = 1.097Γ10β· mβ»ΒΉ. Lyman series (nβ=1): ultraviolet. Balmer series (nβ=2): visible light β four coloured lines. Paschen series (nβ=3): near infrared. Brackett (nβ=4) and Pfund (nβ=5): infrared. Balmer series is most important for NEB exams as it falls in visible range.
What is de Broglie hypothesis in Class 12 Physics?
De Broglie proposed all matter has wave properties: Ξ» = h/mv = h/p. For electron at 10βΆ m/s: Ξ» β 0.7 nm comparable to atomic spacing. This explains Bohr’s quantization only orbits where circumference equals whole number of wavelengths (2Οr = nΞ») are stable, giving exactly Bohr’s angular momentum condition mvr = nh/2Ο.
What is X-ray production in Class 12 Physics?
In Coolidge tube, electrons from hot cathode are accelerated through high voltage (30-150 kV) toward tungsten anode. On collision, electrons produce X-rays by two mechanisms: Bremsstrahlung radiation (continuous spectrum from deceleration) and characteristic X-rays (specific frequencies from knocking out inner shell electrons).
What is Bragg’s law in Class 12 Physics?
Bragg’s law: 2d sinΞΈ = nΞ». When X-rays hit crystal planes, they reflect from successive atomic layers. Constructive interference occurs when path difference 2d sinΞΈ equals whole number of wavelengths. Used to measure X-ray wavelengths (if d known) or determine crystal structure (measure ΞΈ for known Ξ»). Used to discover DNA double helix structure.
What is the difference between excitation and ionization potential?
Excitation potential: voltage that gives electron enough energy to jump to a higher orbit. First excitation potential of hydrogen = 10.2 V (ground state to n=2). Ionization potential: voltage to completely remove electron from atom = 13.6 V for hydrogen. After ionization, the atom becomes a positive ion with no bound electrons remaining.
Which Quantization of Energy topics are most important for Exam?
Most important: energy of nth orbit E_n = β13.6/nΒ² eV (4 marks), spectral series formula with Balmer series (4 marks), radius of nth orbit derivation (4 marks), de Broglie hypothesis (2 marks), Bragg’s law (2 marks). Energy level calculations and spectral line wavelength numericals appear in every NEB board paper.
