MIND GROW Magazine

Electrostatics – Stage 0 (Foundation)

Chapter 1: Electric Charges & Fields – Page 5

1. Why Do Charges Exert Force?

Electric charges exert forces on each other even when separated by space. This interaction is called electrostatic force.

Force acts along the line joining the charges
No physical contact is required

Foundation Idea: Force is transmitted through space via electric field (later concept).

2. Coulomb’s Law (Statement)

The magnitude of electrostatic force between two point charges is:

Directly proportional to the product of charges
Inversely proportional to the square of distance between them

F ∝ q₁ q₂
F ∝ 1 / r²

3. Mathematical Form of Coulomb’s Law

F = k · (q₁ q₂) / r²

F = electrostatic force
q₁, q₂ = point charges
r = distance between charges
k = Coulomb constant

In SI Units: k = 1 / (4πϵ₀)

4. Nature of Force (Attraction or Repulsion)

Like charges → Repulsion
Unlike charges → Attraction

Important: Magnitude depends on values, direction depends on signs.

5. Inverse Square Law – Physical Meaning

If distance between charges is doubled:

F → 1 / 4

If distance is tripled:

F → 1 / 9

JEE Favourite: Inverse-square nature comes from 3D space geometry.

6. Direction of Coulomb Force

The force always acts along the line joining the two charges.

For repulsion → away from each other
For attraction → towards each other

Vector Concept: Force has both magnitude and direction.

7. Point Charges – Meaning

A charge is considered a point charge if:

Its size is negligible compared to separation
Charge is uniformly distributed

JEE Tip: Most problems assume point charges unless stated otherwise.

8. Medium Dependence (Intro Idea)

Electrostatic force depends on the medium between charges.

Maximum in vacuum
Reduced in other media

Later: Permittivity of medium (ϵ) controls force.

Stage 0 – Page 5 Takeaway

Coulomb’s law governs electrostatic force
Force follows inverse square law
Sign of charge controls direction
Magnitude depends on charge & distance

Stage 0 – Page 5 Completed ✅