Which change would result in a stronger electromagnet?
2 answers:
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The question is missing, however, I guess the problem is asking for the value of the force acting between the two balls.
The Coulomb force between the two balls is:
where
is the Coulomb's constant, 
is the intensity of the two charges, and 
is the distance between them.
Substituting these numbers into the equation, we get
The force is repulsive, because the charges have same sign and so they repel each other.
The Coulomb force between the two balls is:
where
Substituting these numbers into the equation, we get
The force is repulsive, because the charges have same sign and so they repel each other.