The Two Laws of Electrostatics

1. Definition

The Two Laws of Electrostatics describe how electric charges interact with each other and how they are distributed:

  • First Law: Like charges repel, unlike charges attract. It States the nature of interaction:

  • Positive ↔ Positive → Repel
  • Negative ↔ Negative → Repel
  • Positive ↔ Negative → Attract

First Law of Electrostatics Diagram

*Second Law: The force between charges is proportional to the product of their charges and inversely proportional to the square of the distance between them (this second law is essentially Coulomb’s Law).

Second Law of Electrostatics Diagram

1.1. Coulom’s Law in Formula Form

Second Law ; Quantitative: F = k · (q₁ · q₂) / r²

Where:

  • F = Electric force between charges
  • k = Coulomb’s constant (≈ 8.99 × 10⁹ N·m²/C²)
  • q₁, q₂ = Magnitudes of the charges (in Coulombs)
  • r = Distance between charges (in meters)

1.2. Other Variations

  • Vector form: F⃗ = k · (q₁ · q₂ / r²) · r̂
  • Repulsive force if q₁ and q₂ have the same sign
  • Attractive force if q₁ and q₂ have opposite signs

Two Laws of Electrostatics Diagram

1.3. Unit of Measurements

  • Force (F): Newton (N)
  • Charge (q): Coulomb (C)
  • Distance (r): meter (m)
  • Coulomb’s constant (k): N·m²/C²

1.4. Example

If q₁ = +5 C, q₂ = -2 C, and r = 0.5 m:

→ F = (8.99 × 10⁹) × (5 × -2) / (0.5²)

→ F = (8.99 × 10⁹ × -10) / 0.25

→ F = (-89.9 × 10⁹) / 0.25

→ F = -359.6 × 10⁹ N

The negative sign shows the force is attractive.

If the result of F is positive then the force is repulsive.

2. Usage

2.1. Calculations

The Two Laws of Electrostatics help you:

  1. Predict whether two charges will attract or repel
  2. Calculate the magnitude of the force between charges
  3. Understand charge behavior in materials and devices

2.2. Applications

They are used in:

  1. Explaining static electricity effects (e.g., clothes sticking after drying)
  2. Designing capacitors and insulation systems
  3. Understanding chemical bonding and atomic structure
  4. Electrostatic precipitators in pollution control

3. Limitations

It is important to note that the Two Laws of Electrostatics have the following limitations:

  1. They apply to stationary charges only
  2. They assume charges are point-like or spherical in distribution
  3. They are accurate only in a uniform medium (unless permittivity adjustments are made)
  4. They don’t account for moving charges (where magnetic effects also occur)

4. Video Explanation

video coming soon