The force of repulsion that two like charges exert on each other is 3.4 N. What will the force be if the distance between the charges is increased to 4 times its original value?

1 Answer
Jan 7, 2016

Let q_1q1 and q_2q2 be the charges, KK be the Coulomb's constant and rr be the distance between the charges when the force is 3.4N3.4N and let FF denote this force.

F=(kq_1q_2)/r^2F=kq1q2r2

implies 3.4=(kq_1q_2)/r^23.4=kq1q2r2

Now, every other condition remains same except the distance between the charges. The distance between the charges has been increased 44 times its original value. Let r' be then new distance between the charges, then
r'=4r
Let the new force between the charges be denoted by F'.
F'=(kq_1q_2)/r_'^2

implies F'=(kq_1q_2)/(4r)^2

implies F'=(kq_1q_2)/(16r^2)

implies F'=(1/16)((kq_1q_2)/r^2)

Since 3.4=(kq_1q_2)/r^2

implies F'=(1/16)(3.4)

implies F'=0.2125N

Hence the force between the two charges becomes 0.2125N