Class 12 Physics Chapter 1 Notes PDF 

📘 Easy Notes for CBSE Board Exams

Welcome students! In this post, you will get easy and complete notes of Class 12 Physics Chapter 1 – Electric Charges and Fields. These notes are useful for:

  • Board exam preparation

  • Quick revision

  • Important formulas

  • Numerical practice

Table of Contents

  1. Electric Charge

  2. Coulomb’s Law

  3. Electric Field

  4. Electric Field Lines

  5. Electric Dipole

  6. Electric Flux

  7. Gauss’s Law

  8. Important Formulas

  9. Important Questions

1. Electric Charge

Electric charge is a basic property of matter due to which objects experience electric force.

Types of Charges

  • Positive Charge (+)

  • Negative Charge (−)

Important Properties

  • Like charges repel each other.

  • Unlike charges attract each other.

  • Charge is conserved.

  • Charge is quantized.

SI Unit

Coulomb (C)

2. Quantization of Charge

The charge on any body is given by:

q = ne

Where:

  • n = integer

  • e = 1.6 × 10⁻¹⁹ C

3. Coulomb’s Law

Coulomb’s law states that the electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of distance between them.

Formula

F = k(q₁q₂/r²)

Where:

  • F = electrostatic force

  • q₁ and q₂ = charges

  • r = distance between charges

  • k = 9 × 10⁹ Nm²/C²

Important Points

  • Like charges repel.

  • Unlike charges attract.

4. Electric Field

The region around a charge where another charge experiences force is called electric field.

Electric Field Intensity

Electric field intensity is the force experienced by a unit positive test charge.

Formula

E = F/q

SI Unit

N/C or V/m

5. Electric Field Due to Point Charge

E = kq/r²

Direction

  • Away from positive charge

  • Towards negative charge

6. Electric Field Lines

Electric field lines are imaginary lines representing electric field direction.

Properties

  1. Start from positive charge and end at negative charge.

  2. Never intersect each other.

  3. Tangent gives direction of electric field.

  4. Closer lines represent stronger field.

7. Electric Dipole

An electric dipole consists of two equal and opposite charges separated by small distance.

Dipole Moment

p = q × 2a

Where:

  • q = charge

  • 2a = separation distance

SI Unit

Coulomb meter (Cm)

8. Electric Flux

Electric flux is the number of electric field lines passing through a surface.

Formula

Φ = EA cosθ

SI Unit

Nm²/C

9. Gauss’s Law

Gauss’s law states that total electric flux through a closed surface is equal to 1/ε₀ times the total charge enclosed.

Formula

∮E·dA = q/ε₀

Important Formulas

Coulomb’s Law

F = k(q₁q₂/r²)

Electric Field

E = F/q

Electric Field Due to Point Charge

E = kq/r²

Dipole Moment

p = q × 2a

Electric Flux

Φ = EA cosθ

Important Board Questions

  1. State Coulomb’s law.
  2. Define electric field intensity.
  3. What is electric dipole?
  4. Define electric flux.
  5. State Gauss’s law.
  6. Write properties of electric field lines.

Preparation Tips

✅ Learn formulas carefully
✅ Practice numerical questions daily
✅ Draw neat diagrams
✅ Revise derivations
✅ Write SI units correctly


Comments

Post a Comment