Pith balls repel each other
Slide a charged (−ve) rod over one of the pith balls when they are in contact with each other,
this negative charge will spread out uniformly over both surfaces, and in turn repel each other.
Coulomb's Law is a law stating the force between two charges is proportional to the amount of charge on both charges and inversely proportional to the square of the distance between them.
In general, any two charged objects will create a force on each other. Opposite charges will produce an attractive force while similar charges will produce a repulsive force. The greater the charges, the greater the force. The greater the distance between them, the smaller the force. The forces are force pairs of each other so they will always be equal in size and opposite in direction.
This law states that the force between the charges is inversely proportional to the distance between them, i.e., Coulomb's law obeys Inverse square law.
The Quantity of charge can be measured in either elementary charges (an elementary charge is the amount of charge on one electron or proton) or in Coulombs. An elementary charge is a very tiny unit of charge. Since it is so small it is not usually a convenient unit to measure typical amounts of charge. It would be similar to measuring distances from one town to the next, in millimeters.
On the other hand, a coulomb is an incredibly large unit of charge. It is actually too large a unit of charge
for talking about electrostatics (stationary charges) but it is an appropriately sized unit as we begin describing the quantity
of charge moved in an electric circuit.
1Coulomb = 6.3×1018 elementary charges
(or)
1elementary charge = 1.6×10− 19 Coulomb
The quantity of Charge is always measured in Coulombs.