Point charges 10 micro coulomb and 20 micro coulomb are separated by distance r.additional charge of 8 micro coulomb is given to each.by what factor the force between them will change

We have, Initial charges are 10 × 10-6 C and 20 × 10-6 C. Suppose they are separated by distance ‘r’. Now,

(9 × 109)×(10 × 10-6)×(20 × 10-6)/r2 = F

Now, the new charges are [(10+8) × 10-6 C] and [(20+8) × 10-6 C] or (18 × 10-6 C) and (28 × 10-6 C). The new force between the two is,

F’ = (9 × 109)×(18 × 10-6)×(28 × 10-6)/r2

Now you can find ratio.

Regards

Arun