The principle of superposition is to calculate the electric force experienced by a charge q1 due to other charges q2, q3 ……. qn.
The total force on a given charge is the vector sum of the forces exerted on it due to all other charges.
The force on q1 due to q2
Vector F12 = k q1 q2 / (r21)^2 (r21 cap)
similarly, force on q1 due to q3
Vector F21 = k q1 q2 / (r31)^2 (r31 cap)
The total force F1 on the charge q1 by all other charges is,
Vector F1 = Vector [F12+F13+F14+.........+F1n]
So
Vector F1=1/4πεo[q1q2/r21^2 (r21cap) + q1q3/r31^2 (r31cap) + ..... + q1q n/r n1^2 (r n1 cap )]
Note:
A torsion balance is a sensitive device to measure force. It was also used later by Cavendish to measure the very feeble gravitational force between two objects, to verify Newton’s Law of Gravitation.
