Question

Two identical metal spheres carry charges of +q and -2q respectively. When the spheres are separated by a
large distance r , the force between them is F. Now the spheres are allowed to touch and then move back to the same separation. Find the new force of repulsion between them.

Answer 1

two charges = +q and -2q
distance =r
now, we know that
k
$k2 {q}^{2} \div {r}^{2} = f$
now the sphere are allow to touch then the charge of each sphere is
$q - 2q \div 2 = - q \div 2$
then the repulsive force is
$k {q}^{2} \div 4 \div {r}^{2}$
$f \div 4$