Physics... Electricity

Question

A 4N force acts between two equal charge separated by a distance d.  What will be the new force if the magnitude of each of the two charges are doubled but the distance remains the same?  

	16N
	8N
	2N
	1N

Answer 1

Consider Coulomb's law F = k Q1Q2 / d². The force is proportional to the product of the charges. If the charges are equal, the force expression becomes k Q² / d². If we double each charge, the new charge can be expressed as 2Q. As the force is proportional to the product of the charges as already stated, the product of the new charges will be 4Q (2Q x 2Q), so the force will be quadrupled, and the new force is 16N.