2. What is the charge, expressed in micro coulombs on two equally and similarly charges spheres placed in air with their centres 30 cm apart repelling each other with a force of 120 mgm.

q = 0.1086 micro Coulombs

Explanation:

By Coulombs law, we have;

Where;

F = The electric force = 120 mgm

q₁ and q₂ = Charge

r = The separating distance = 30 cm = 0.3 m

k = 8.9876×10⁹ kg·m³/(s²·C²)

Where, q₁ and q₂, we have;

Whereby the force is the force of 120 milligram mass, we have;

0.00012 × 9.81 = 000011772 N

Substituting the values, we have;

q = 0.1086 micro Coulombs.