"The electric force (coulombian force) between two stationary point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them."
⇒ According to the law of electric force between the two point charges q1 and q2, seperated by a distance r can be given as under:
F ∝ q1q2/r2
∴ F = k q1q2/r2
Where,
K = proportionality constant ≈ 9 x 109 Nm2C-2
⇒ In many formulas of electricity, k is replaced by 1/4Πε0 to avoid writing a factor of 4Π, when ε0 is the electrical permitivity of free space.
ε0 = 8.854185 x 10-12 ≈ 8.9 x 10-12 C2N-1m-2
Hence, F = 1/4Πε0 X q1q2/r2
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