Two insulated charged copper spheres A and B have their centres separated by a distance of 0.5 m. The charge on each spheres is `6.5xx10^(-7)C`. A third sphere c of identifical shape and size is brought in contanct with A and them brought in contact with B and finally removed. What is the new force between A and B?

Explanation

Initial charge on A an B `q_(A)=q_(B)=6.5xx10^(-7)C`
When an uncharged conductor C is brought in contact with A, then charge on A and C will be `3.25xx10^(-7)C`. When `C` is brought in contanct with B
Charge on C and B will be `(3.25xx10^(-7)+6.50xx10^(-7))/2=4.875xx10^(-7)C`
The force of repulsion betwen `3.25xx10^(-7)C` (on A) and
`4.875xx10^(-7)C` (on C)`=(9xx10^(9)xx3.25xx10^(-7)xx4.875xx10^(-7))/((0.5)^(2))=5.7xx10^(-3)N`
The new force between A and B is `5.7xx10^(-3)N`