Physics (Class 12) — Free Notes (CBSE & HBSE)
Free Class 12 Physics notes with NCERT solutions, board sample papers, previous year question papers (PYQs), important MCQs and chapter-wise revision — Electrostatics, Magnetism, Optics, Modern Physics. CBSE/HBSE board + JEE Main + NEET aligned.
Free, chapter-wise Physics notes for Class 12 on Siksha Sarovar, aligned to NCERT and both CBSE and Haryana Board (HBSE). Covers 14 chapters with explanations, worked examples and board-pattern practice questions.
Chapters covered (14)
- Electric Charges and Fields — CBSE emphasizes Gauss's law derivations, superposition principle, and electric field for symmetric charge distributions with analytical problems. HBSE focuses on Coulomb's law…
- Electrostatic Potential and Capacitance — CBSE emphasizes derivation of potential energy, capacitor combinations, effect of dielectrics, and energy density. HBSE focuses on definition of potential, capacitance formula,…
- Current Electricity — CBSE focuses on drift velocity derivation, Kirchhoff's laws with complex circuit problems, and potentiometer applications. HBSE emphasizes Ohm's law, resistivity, temperature…
- Moving Charges and Magnetism — CBSE emphasizes Biot-Savart law derivations, Ampere's law applications, motion of charged particles, and galvanometer conversion. HBSE focuses on force on current-carrying…
- Magnetism and Matter — CBSE focuses on derivation of axial and equatorial fields of bar magnet, earth's magnetism parameters, and classification of magnetic materials with susceptibility. HBSE…
- Electromagnetic Induction — CBSE focuses on Faraday's law derivation, Lenz's law, motional EMF calculation, self and mutual inductance derivations, and energy stored in inductor. HBSE emphasizes Faraday's…
- Alternating Current — CBSE emphasizes phasor diagrams, series LCR resonance derivation, power factor, and transformer efficiency calculations. HBSE focuses on RMS and peak values, reactance…
- Electromagnetic Waves — CBSE focuses on Maxwell displacement current derivation, EM wave properties including c=1/sqrt(e0m0), and the EM spectrum applications. HBSE tests displacement current, transverse…
- Ray Optics and Optical Instruments — CBSE emphasizes mirror and lens formulas, total internal reflection, prism dispersion, and microscope/telescope magnification derivations. HBSE focuses on numerical problems with…
- Wave Optics — CBSE focuses on Huygens' principle, Young's double slit derivation, interference conditions, diffraction, and Malus's law for polarisation. HBSE emphasizes coherent sources,…
- Dual Nature of Radiation and Matter — CBSE emphasizes Einstein's photoelectric equation derivation, stopping potential, de Broglie hypothesis, and Davisson-Germer experimental evidence. HBSE focuses on photoelectric…
- Atoms — CBSE focuses on Rutherford's scattering experiment and model limitations, all four Bohr's postulates, derivation of radii and energy levels, and hydrogen spectrum series. HBSE…
- Nuclei — CBSE focuses on binding energy per nucleon graph, radioactive decay law derivation, half-life, nuclear fission and fusion processes. HBSE emphasizes nuclear composition,…
- Semiconductor Electronics — CBSE focuses on energy band theory, p-n junction formation, depletion layer, I-V characteristics, rectification, transistor action in CE configuration, and logic gates. HBSE…
Electric Charges and Fields: Coulomb's Law and Electric Charge
Electric Charge
Electric charge is a fundamental scalar property of matter that causes it to experience a force in an electromagnetic field. It exists in two types: positive (protons) and negative (electrons). The SI unit is Coulomb (C).
Properties of Electric Charge
| Property | Description |
|---|---|
| Quantization | q = ne, where n = ±1, ±2, ... and e = 1.6×10⁻¹⁹ C |
| Conservation | Total charge in an isolated system remains constant |
| Additivity | Total charge = algebraic sum of all individual charges |
| Invariance | Charge is independent of velocity (unlike mass) |
Coulomb's Law
The electrostatic force between two point charges q₁ and q₂ separated by distance r in vacuum:
F = kq₁q₂/r²
where k = 1/(4πε₀) = 9×10⁹ N·m²/C²
ε₀ = permittivity of free space = 8.854×10⁻¹² C²·N⁻¹·m⁻²
Vector form: F⃗₁₂ = (q₁q₂/4πε₀r²) r̂₁₂
- Positive F → repulsion; Negative F → attraction
Coulomb's Law in a Medium
In a medium with dielectric constant K:
F_medium = kq₁q₂/(Kr²) = q₁q₂/(4πε₀εᵣr²)
where εᵣ = K = ε/ε₀ is the relative permittivity of the medium.
Comparison: Coulomb vs Gravitational Force
| Feature | Coulomb Force | Gravitational Force |
|---|---|---|
| Source | Electric charge | Mass |
| Nature | Attractive or Repulsive | Always Attractive |
| Constant | k = 9×10⁹ N·m²/C² | G = 6.67×10⁻¹¹ N·m²/kg² |
| Ratio Fc/Fg (H atom) | ~2.27×10³⁹ | 1 |
| Medium effect | Reduced by factor K | Not affected |
| Range | Long range (1/r²) | Long range (1/r²) |
Coulomb force is approximately 10³⁹ times stronger than gravity.
Superposition Principle
The net electric force on a charge due to multiple charges is the vector sum of all individual Coulomb forces:
F⃗_net = F⃗₁ + F⃗₂ + F⃗₃ + ...
Each pair interaction is independent of the presence of other charges.
Continuous Charge Distributions
| Type | Symbol | Formula | Unit |
|---|---|---|---|
| Linear | λ | λ = dq/dl | C/m |
| Surface | σ | σ = dq/dA | C/m² |
| Volume | ρ | ρ = dq/dV | C/m³ |
Charging Methods
- Friction: Electrons transfer between rubbed materials (e.g., glass rod + silk)
- Conduction: Direct contact with charged body
- Induction: Nearby charged body redistributes charges without contact
Diagram Indicator: [Two point charges q₁ and q₂ separated by distance r; arrows showing F₁₂ (force on q₂ due to q₁) and F₂₁ (force on q₁ due to q₂) for both attraction and repulsion cases. Unit vector r̂₁₂ labeled.]
Frequently asked questions
Are these Physics notes free?
Yes — all Physics notes on Siksha Sarovar are free to read, no account required.
Do the notes follow CBSE and HBSE?
Yes. Notes are NCERT-aligned and include both CBSE and Haryana Board (HBSE) exam guidance, important questions and MCQs.
Can I prepare for board exams here?
Yes — each chapter includes key concepts, formulas, important questions and practice MCQs for board exam revision.