12.1 COULOMB’S LAW COULOMB’S LAW Statement : The electrostatic force between two point charges is directly proportional to the product of the magnitude of charges and inversely proportional to the square of distance between them. Mathematical Expression : If two point charges q 1 and q 2 are separated by a distance r , then the electrostatic force ‘ F ’ between them is expressed as: F = k q 1 q 2 r 2 where k is the constant of proportionality and is expressed as k = 1 4 π ε 0 where ε 0 is the permittivity of free space and its value in SI unit is 8 . 85 × 10 − 12 C 2 N m 2 . VECTOR FORM OF COULOMB'S LAW The electrostatic force F ⃗ between two point charges ‘ q 1 ’ to ‘ q 2 ’ is expressed as: F ⃗ = 1 4 π ε 0 q 1 q 2 r 2 r ˆ Here...