The magnitude of the electrostatic force between two charges is given by:

where
ke is the Coulomb's constant
q1 and q2 are the two charges
r is the separation between the two charges
We can see that the magnitude of the force is directly proportional to the charges. This means that when one of the charges is doubled, the magnitude of the electrostatic force will double as well, so the correct answer is
A) <span>The magnitude of the electrostatic force doubles</span>
Static Friction
It is the friction that exists between a stationary object and the surface on which it's resting.
Sliding friction
It is the resistance created by two objects sliding against each other.
Rolling friction:-
It is the force resisting the motion when a body rolls on a surface.
hope this helps x
To get a uniform field in the central region between the coils, current flows in the same direction in each.