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Class 12 PhysicsChapter Notes

2 chapters · Definitions, key points, formulas & exam tips · Updated 2025-26

Ch 1

Electric Charges and Fields

Key Definitions

Electric Charge: A fundamental property of matter. Two types: positive and negative. Unit: Coulomb (C).

Coulomb's Law: Force between two point charges: F = kq₁q₂/r². Directly proportional to product of charges, inversely to square of distance.

Electric Field: Force per unit positive charge at a point. E = F/q. Unit: N/C or V/m.

Key Points to Remember

→Charge is quantised: q = ne where e = 1.6 × 10⁻¹⁹ C.
→Charge is conserved — total charge in an isolated system remains constant.
→Electric field lines: start from positive, end at negative charge. Never cross.
→Gauss's Law: total electric flux through a closed surface = q/ε₀.
→Electric field inside a conductor = 0.
→Field due to infinite plane sheet of charge: E = σ/2ε₀.

Formulas & Equations

F = kq₁q₂/r² = q₁q₂/(4πε₀r²)

E = F/q = kq/r²

Electric flux: Φ = E·A cosθ

Gauss's Law: Φ = q_enclosed/ε₀

Exam Tips

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Principle of superposition: net force = vector sum of individual forces.

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Electric dipole: two equal and opposite charges separated by distance 2l. p = q × 2l.

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Torque on dipole in field: τ = pE sinθ.

Ch 2

Electrostatic Potential and Capacitance

Key Definitions

Electric Potential: Work done per unit positive charge in bringing it from infinity to a point. Unit: Volt (V).

Capacitance: Ability to store charge. C = Q/V. Unit: Farad (F).

Dielectric: Insulating material between capacitor plates that increases capacitance.

Key Points to Remember

→Equipotential surface: potential is same at all points. Field is perpendicular to it.
→Work done in moving charge on equipotential surface = 0.
→Capacitors in series: 1/C = 1/C₁ + 1/C₂. In parallel: C = C₁ + C₂.
→Energy stored: U = ½CV² = Q²/2C = QV/2.
→Dielectric increases capacitance by factor K (dielectric constant).
→Van de Graaff generator: accumulates high voltage using electrostatic principles.

Formulas & Equations

V = kq/r

C = ε₀A/d (parallel plate)

Energy: U = ½CV²

With dielectric: C = Kε₀A/d

Exam Tips

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Potential due to a dipole: V = kp cosθ/r² — direction matters.

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Common capacitor questions: find equivalent capacitance of networks.

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Effect of inserting dielectric: if battery connected — charge increases, V unchanged; if disconnected — V decreases, charge unchanged.

Frequently Asked Questions

Are these notes based on 2025-26 CBSE syllabus for Class 12 Physics?

Yes. All chapter notes here are based on the latest 2025-26 CBSE syllabus for Class 12 Physics. Deleted topics are clearly marked so you focus only on what will be tested in your board exam.

How to study Class 12 Physics notes effectively for board exams?

Read each chapter's notes once to build understanding. Then close the notes and try to recall every key point, definition, and formula from memory. Anything you miss is your weak area — revisit only those points. This active recall method takes less time and retains far more than re-reading.

What is the difference between NCERT notes and chapter summaries?

Chapter notes contain detailed definitions, key terms, formulas, and concept breakdowns — they're for learning and understanding. Chapter summaries are shorter paragraph-style overviews — they're for quick revision. Use notes when you're studying a chapter for the first time; use summaries the night before the exam.

Do I need to memorise formulas for Class 12 Physics CBSE board exam?

Yes. Formulas listed in these notes must be memorised precisely — CBSE doesn't give formula sheets during exams. Write each formula 5–10 times, then recall it without looking. In the exam, write the formula first, then substitute values — this helps you earn partial marks even if the final answer has a calculation error.

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