Force of the charge

Question

Two charges of 10^-6 C are located 1cm apart (a) What is the force on a charge +10^-8 halfway between them? (b) What is the force on a charge of -10^-8 C at the same place?

 

Answer 1

In both cases the net force is zero because the third charge is exactly in the  middle between 2 equal charges.  In part (a), the 10^-8 C charge is repelled equally to the right and left by the 2 positive charges, so the net force is zero.  In part (b), the -10^-8 C charge is attracted equally to the left and the right by the 2 positive charges, so the net force is zero.  You can compute the net force in both cases using Coulomb's law and see that you get zero.