Two point charges \( q_1 = 4 \, \mu\text{C} \) and \( q_2 = -6 \, \mu\text{C} \) are placed 20 cm apart in vacuum. What
**Superposition principle** asserts net Coulomb force on charge equals vector sum of forces from each other charge independently, F_net = Σ F_i, where F_i = k q q_i/r_i² r̂_i. In equilateral triangle or square symmetry, components may cancel at centroid, producing equilibrium. Using Coulomb's law: F = k (|q₁ q₂|/r²) . Given: k = 9 × 10⁹ N·m²/C² , q₁ = 4 × 10⁻⁶ C , q₂ = -6 × 10⁻⁶ C , r = 0.2 m . Magnitude: |q₁ q₂| = (4 × 10⁻⁶) × (6 × 10⁻⁶) = 24 × 10⁻¹² C² . r² = (0.2)² = 0.04 m² . F = 9
Ref: NCERT > Physics Book > Electric Charges and Fields > Superposition Principle and Equilibrium of Charges