Question

Two charges that are separated by one meter exert 1-n forces on each other. if the magnitude of each charge is doubled, the force on each charge is

Answer 1

The electrostatic force between the two charges is
$F=k_E \frac{q_1 q_2}{r^2}$
where q1 and q2 are the magnitudes of the two charges, and r the distance between them.

We can see from the formula that F is proportional to the product between the two charges:
$F \sim q_1 q_2$
so, if the magnitude of each charge is doubled, the new force will get a factor 4:
$F' \sim (2 q_1 )(2 q_2 )=4 q_1 q_2 =4 F$
So, the new force will be 4 times the original force:
$F' = 4 \cdot 1N= 4N$