In: Physics
Two identical insulated metal spheres are separated d metres apart and carry charges of +q and –q. The force that they exert on each other is 4 x 10-3 N. If the charged spheres are now separated by 3d metres, the magnitude of the new force between them is:
q = magnitude of charge on each sphere
ri = distance between the two charges initially = d
Fi = force between the two charges initially = 4 x 10-3 N
rf = distance between the two charges finally = 3d
Ff = force between the two charges finally = ?
Using coulomb's law, we have
Fi = k q2/ri2 Eq-1
similarly, for final force, we have
Ff = k q2/rf2 Eq-2
Dividing Eq-2 by Eq-1
Ff /Fi = (k q2/rf2) / (k q2/ri2)
Ff /Fi = (q2/rf2) (ri2/q2)
Ff /Fi = ri2/rf2
Ff /(4 x 10-3) = (d/(3d))2
Ff = (4 x 10-3) /9
Ff = 4.44 x 10-4 N